[Federal Register Volume 67, Number 74 (Wednesday, April 17, 2002)]
[Proposed Rules]
[Pages 19030-19090]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 02-9154]
[[Page 19029]]
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Part III
Environmental Protection Agency
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40 CFR Part 141
National Primary Drinking Water Regulations; Announcement of the
Results of EPA's Review of Existing Drinking Water Standards and
Request for Public Comment; Proposed Rule
Federal Register / Vol. 67, No. 74 / Wednesday, April 17, 2002 /
Proposed Rules
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 141
[FRL-7167-9]
RIN 2040-AD67
National Primary Drinking Water Regulations; Announcement of the
Results of EPA's Review of Existing Drinking Water Standards and
Request for Public Comment
AGENCY: Environmental Protection Agency (EPA).
ACTION: Review of regulations; request for comments.
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SUMMARY: The Safe Drinking Water Act (SDWA) requires the United States
Environmental Protection Agency (EPA) to conduct a periodic review of
existing National Primary Drinking Water Regulations (NPDWRs). EPA is
requesting public comment on the results of its review of 69 NPDWRs
that were established prior to 1997, including 68 chemical NPDWRs and
the Total Coliform Rule (TCR). The intended purpose of the review is to
identify those NPDWRs for which current health risk assessments,
changes in technology, and/or other factors, provide a health or
technical basis to support a regulatory revision that will improve or
strengthen public health protection. Based on its review, and pending
an evaluation of public comments, the Agency preliminarily believes
that the 68 chemical NPDWRs remain appropriate at this time, and that
the TCR should be revised.
DATES: EPA must receive public comments on this action by June 17,
2002.
ADDRESSES: Please send your comments to the W-01-14 Comments Clerk.
Submit electronic comments to: [email protected]. Written comments
should be mailed to: Water Docket (MC-4101), U.S. Environmental
Protection Agency, 1200 Pennsylvania Avenue, NW., Washington, DC,
20460. Hand deliveries should be delivered to EPA's Water Docket at
East Tower Basement (EB Room 57), Waterside Mall, 401 M Street, SW.,
Washington, DC, 20460. You may contact the docket at (202) 260-3027
between 9 a.m. and 3:30 p.m. Eastern Time, Monday through Friday.
Comments may be submitted electronically. See SUPPLEMENTARY INFORMATION
for file formats and other information about electronic filing and
docket review.
FOR FURTHER INFORMATION CONTACT: For technical inquiries contact: Judy
Lebowich, (202) 564-4884, e-mail: [email protected], or Wynne
Miller, (202) 564-4887, e-mail: [email protected]. For general
information about, and copies of, this document or information about
the existing NPDWRs discussed in this action, contact the Safe Drinking
Water Hotline. Callers within the United States may reach the Hotline
at (800) 426-4791. The Hotline is open Monday through Friday, excluding
Federal holidays, from 9 a.m. to 5:30 p.m. Eastern Time.
SUPPLEMENTARY INFORMATION:
How Should I Submit Comments on This Action?
EPA will accept written or electronic comments (please do not send
both). EPA prefers electronic comments. Commenters should use a
separate paragraph for each issue discussed. No facsimiles (faxes) will
be accepted. Commenters who want EPA to acknowledge receipt of their
comments should also send a self-addressed, stamped envelope. If you
submit written comments, please submit an original and three copies of
your comments and enclosures (including references).
Electronic comments must be submitted in WordPerfect 8 (or an older
version) or ASCII file format. Compressed or zipped files will not be
accepted. You may file electronic comments on this action online at
many Federal Depository Libraries.
The Agency's response-to-comments document for the final decision
will address the comments received on this action, and the response-to-
comments document will be made available in the docket.
How Can I Obtain Materials in the Docket?
The docket is available for inspection from 9:00 a.m. to 4:00 p.m.,
Monday through Friday, excluding legal holidays, at the Water Docket,
East Tower Basement (EB Room 57), Waterside Mall, USEPA, 401 M Street,
SW; Washington, DC. For access to docket (Docket Number W-01-14)
materials, please call (202) 260-3027 between 9:00 a.m. and 3:30 p.m.,
Eastern Time, Monday through Friday, to schedule an appointment.
Does This Action Apply to My Public Water System?
This action itself does not impose any requirements on anyone.
Instead, it notifies interested parties of EPA's preliminary revise/not
revise decisions for 69 NPDWRs.
Abbreviations and Acronyms Used in This Action
>--greater than
2,4-D--2,4-dichlorophenoxyacetic acid
AA--activated alumina
AI--adequate intake
ASDWA--Association of State Drinking Water Administrators
ATSDR--Agency for Toxic Substances and Disease Registry
AWWA--American Water Works Association
BAT--best available technology
BMD--benchmark dose
bw--body weight
CCL--Contaminant Candidate List
CFR--Code of Federal Regulations
CMR--Chemical Monitoring Reform
CWS--community water system
DBCP--1,2-dibromo-3-chloropropane
DBPR--Disinfectants and Disinfection Byproducts Rule
DEHA--di(2-ethylhexyl)adipate
DEHP--di(2-ethylhexyl)phthalate
DRI--dietary reference intake
DWEL--drinking water equivalent level
EDB--ethylene dibromide
EPA--U.S. Environmental Protection Agency
EPTDS--entry points to a distribution system
FR--Federal Register
GAC--granular activated carbon
GC/MS--gas chromatography/mass spectrometry
HHS--Department of Health and Human Services
HPC--heterotrophic plate count
I--daily drinking water intake
IESWTR--Interim Enhanced Surface Water Treatment Rule
IRIS--Integrated Risk Information System
LCR--Lead and Copper Rule
LOAEL--lowest-observed-adverse-effect level
LT1ESWTR--Long-Term 1 Enhanced Surface Water Treatment Rule
LT2ESWTR--Long-Term 2 Enhanced Surface Water Treatment Rule
MCL--maximum contaminant level
MCLG--maximum contaminant level goal
M/DBP--Microbial/Disinfection Byproducts
MDL--method detection limit
MF--modifying factor
MFL--million fibers per liter
mg/kg/day--milligrams per kilogram of body weight per day
mg/L--milligrams per liter
MSRC--Mercury Study Report to Congress
MTD--maximum tolerated dose
N--nitrogen
NAS--National Academy of Sciences
NCOD--National Drinking Water Contaminant Occurrence Database
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NDWAC--National Drinking Water Advisory Council
NIPDWR--National Interim Primary Drinking Water Regulation
NOAEL--no-observed-adverse-effect level
NPDWR--National Primary Drinking Water Regulation
NRC--National Research Council
NTNCWS--non-transient, non-community water system
NTP--National Toxicology Program
NWIS--National Water Information System
OGWDW--Office of Ground Water and Drinking Water
OPP--Office of Pesticide Programs
OW--Office of Water
PAC--powdered activated carbon
PCBs--polychlorinated biphenyls
POU--point-of-use
ppm--part per million
PQL--practical quantitation level
PTA--packed tower aeration
PWS--public water system
RDA--recommended dietary allowance
RfD--reference dose
RO--reverse osmosis
RSC--relative source contribution
SAB--Science Advisory Board
SDWA--Safe Drinking Water Act
SDWIS--Safe Drinking Water Information System
SMCL--secondary maximum contaminant level
SOC--synthetic organic chemical
SWTR--Surface Water Treatment Rule
TCR--Total Coliform Rule
TNCWS--transient, non-community water system
TT--treatment technique
TTHM--total trihalomethanes
UF--uncertainty factor
UL--tolerable upper intake level
URCIS--Unregulated Contaminant Information System
VOC--volatile organic chemical
WS--water supply
Table of Contents
I. Background and Summary of Today's Action
A. What are the Statutory Requirements for the Six-Year Review?
B. What is the Schedule for Reviewing Existing NPDWRs?
II. Stakeholder Involvement in the Six-Year Review Process
A. How Have Stakeholders Been Involved in the Review Process?
B. How Does EPA Plan to Involve the Science Advisory Board
(SAB)?
III. Regulations Included in the Six-Year Review
IV. EPA's Protocol for Reviewing the NPDWRs Included in Today's
Action
A. What was EPA's Review Process?
1. Initial Technical Review
2. In-Depth Technical Review
B. How Did EPA Review the Chemical NPDWRs?
1. Health Effects
2. Analytical Feasibility
3. Treatment Feasibility
4. Other Regulatory Revisions
5. Occurrence and Exposure Analysis
6. Economic Considerations
C. How Is EPA Reviewing the Total Coliform Rule?
D. How Did EPA Factor Children's Health Concerns into the
Review?
V. EPA's Preliminary Decisions Based on its Review of NPDWRs
Included in Today's Action
A. What Preliminary Decisions Has EPA Made Regarding the
Chemical NPDWRs?
1. Acrylamide
2. Alachlor
3. Antimony
4. Asbestos
5. Atrazine
6. Barium
7. Benzene
8. Benzo[a]pyrene
9. Beryllium
10. Cadmium
11. Carbofuran
12. Carbon Tetrachloride
13. Chlordane
14. Chromium
15. Copper
16. Cyanide
17. 2,4-D (2,4-Dichlorophenoxyacetic Acid)
18. Dalapon (2,2-Dichloropropionic Acid)
19. 1,2-Dibromo-3-chloropropane (DBCP)
20. 1,2-Dichlorobenzene (o-Dichlorobenzene)
21. 1,4-Dichlorobenzene (p-Dichlorobenzene)
22. 1,2-Dichloroethane (Ethylene Dichloride)
23. 1,1-Dichloroethylene
24. cis-1,2-Dichloroethylene
25. trans-1,2-Dichloroethylene
26. Dichloromethane (Methylene Chloride)
27. 1,2-Dichloropropane
28. Di(2-ethylhexyl)adipate (DEHA)
29. Di(2-ethylhexyl)phthalate (DEHP)
30. Dinoseb
31. Diquat
32. Endothall
33. Endrin
34. Epichlorohydrin
35. Ethylbenzene
36. Ethylene Dibromide (EDB; 1,2-Dibromoethane)
37. Fluoride
38. Glyphosate
39. Heptachlor
40. Heptachlor Epoxide
41. Hexachlorobenzene
42. Hexachlorocyclopentadiene
43. Lead
44. Lindane (-Hexachlorocyclohexane)
45. Mercury (Inorganic)
46. Methoxychlor
47. Monochlorobenzene (Chlorobenzene)
48. Nitrate (as N)
49. Nitrite (as N)
50. Oxamyl (Vydate)
51. Pentachlorophenol
52. Picloram
53. Polychlorinated Biphenyls (PCBs)
54. Selenium
55. Simazine
56. Styrene
57. 2,3,7,8-TCDD (Dioxin)
58. Tetrachloroethylene
59. Thallium
60. Toluene
61. Toxaphene
62. 2,4,5-TP (Silvex; 2,4,5-Trichlorophenoxypropionic Acid)
63. 1,2,4-Trichlorobenzene
64. 1,1,1-Trichloroethane
65. 1,1,2-Trichloroethane
66. Trichloroethylene
67. Vinyl Chloride
68. Xylenes (Total)
B. What Preliminary Decision Has EPA Made Regarding the Total
Coliform Rule?
1. Background
2. Technical Reviews
3. Preliminary Decision
VI. Request for Comments
A. On Which Issues is EPA Soliciting Public Comment?
B. Request for Comments on Use of Plain Language
VII. EPA's Next Steps
VIII. References
Appendix A: Background on the Calculation of MCLG and Cancer
Classification System
List of Tables
Table III-1: Pre-1997 NPDWRs Included in Today's Action
Table III-2: NPDWRs Not Included in Today's Action
Table IV-1: Summary of the Outcome of the Six-Year Health Effects
Review
Table IV-2: Chemical NPDWRs Included in the Analytical Feasibility
Reassessment and the Result of that Assessment
Table IV-3: Chemical NPDWRs Included in the Treatment Feasibility
Analysis
Table V-1: Preliminary Revise/Not Revise Decisions for the 68
Chemical NPDWRs and TCR
Table V-2: Benzene Occurrence
Table V-3: Beryllium Occurrence
Table V-4: Chlordane Occurrence
Table V-5: Chromium Occurrence
Table V-6: 1,2-Dibromo-3-chloropropane Occurrence
Table V-7: Dichloromethane Occurrence
Table V-8: 1,2-Dichloropropane Occurrence
Table V-9: Heptachlor Occurrence
Table V-10: Heptachlor Epoxide Occurrence
Table V-11: Hexachlorobenzene Occurrence
Table V-12: Oxamyl Occurrence
Table V-13: Picloram Occurrence
Table V-14: Toxaphene Occurrence
Table V-15: 1,1,2-Trichloroethane Occurrence
Table VI-1: Issues on Which EPA is Requesting Public Comment or Data
Table A-1: Cancer Classification Systems Used by EPA
List of Figures
Figure 1: Overview of the Protocol for the Revise/Not Revise
Decision
Figure 2: Distribution of State Rankings: Manufacturing
Establishments per Square Mile vs. Total Farm Agricultural Chemical
Expenses
Figure 3: Geographic Distribution of the 16-State Cross-Section Used
for Occurrence Analysis
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I. Background and Summary of Today's Action
A. What Are the Statutory Requirements for the Six-Year Review?
Under the SDWA, as amended in 1996, EPA must periodically review
existing national primary drinking water regulations (NPDWRs) and, if
appropriate, revise them. Section 1412(b)(9) of SDWA states:
The Administrator shall, not less often than every 6 years,
review and revise, as appropriate, each national primary drinking
water regulation promulgated under this title. Any revision of a
national primary drinking water regulation shall be promulgated in
accordance with this section, except that each revision shall
maintain, or provide for greater, protection of the health of
persons.
Pursuant to the SDWA 1996 Amendments, EPA developed a systematic
approach, or protocol, for the review of NPDWRs discussed in today's
action. EPA has applied the protocol discussed in section IV of today's
action to the Agency's initial Six-Year Review of NPDWRs for total
coliforms and 68 inorganic and organic chemicals, published prior to
the SDWA 1996 Amendments (i.e., pre-1997 NPDWRs). Section III of
today's action identifies these NPDWRs and section V of today's action
contains a summary of the review findings for each of these 69 NPDWRs
(see Table III-1).
While the Agency expects that modifications to the protocol will be
made in subsequent six-year reviews to address changing circumstances,
the Agency expects to use the framework developed for the current
review as the starting point. EPA, therefore, is seeking public comment
on the protocol that has been applied to the current review.
B. What Is the Schedule for Reviewing Existing NPDWRs?
EPA plans to publish its final findings with respect to the initial
review of these 69 NPDWRs in the Federal Register (FR) in the August
2002 time frame.
In addition to these 69 NPDWRs, there are additional pre-1997
NPDWRs, which are being or have been reviewed separately from today's
action. Section III explains how the Agency plans to satisfy the Six-
Year Review requirement for those regulations. In most cases, EPA has
performed or is performing the review in conjunction with recent or
ongoing rulemakings. NPDWRs published after the 1996 SDWA Amendments
will be reviewed as a part of the 2002-2008 review cycle.
II. Stakeholder Involvement in the Six-Year Review Process
A. How Have Stakeholders Been Involved in the Review Process?
Stakeholders include:
The general public;
Congress;
Other Federal agencies;
State, Tribal, and local officials;
Public health/health care providers;
Public interest groups;
Public water suppliers;
National trade associations;
Environmental groups;
Manufacturers; and
Agricultural producers.
EPA involved stakeholders by: holding a stakeholder meeting;
participating in national meetings, workshops, and technical forums;
meeting informally with associations and technical experts; posting
information on the Office of Ground Water and Drinking Water's
(OGWDW's) web page (www.epa.gov/safewater/); and publishing this FR
notice on the Six-Year Review.
EPA invited representatives from State and Tribal communities,
public water systems (PWSs), public health organizations, academia,
environmental and public interest groups, engineering firms, and other
stakeholders to a stakeholder meeting in Washington, DC, in November
1999 (64 FR 55711, October 14, 1999 (USEPA, 1999c)). Approximately 50
participants attended, including representatives from the invited
groups. EPA discussed its preliminary strategy for the Six-Year Review
and invited stakeholder comment. Stakeholders generally agreed that EPA
had identified the appropriate key elements for the review; however, in
some cases, stakeholders suggested that EPA needed to be more proactive
in seeking out new information that might affect the regulatory
decision (USEPA, 1999e). For more detailed information about this
stakeholder meeting, the docket for this action (Docket Number W-01-14)
contains the stakeholder meeting discussion papers, the agenda, the
participant list, presentation materials, and an executive meeting
summary which includes the specific comments and questions posed by
stakeholders. The executive meeting summary is also available on EPA's
drinking water web page, http://www.epa.gov/safewater/ccl/novmtg.html.
In the Spring of 2000, the National Drinking Water Advisory Council
(NDWAC) formed a working group to develop recommendations regarding the
process the Agency should apply to conduct a periodic and systematic
review of existing NPDWRs. The Working Group held two meetings and a
conference call during June through September 2000 (USEPA, 2000b;
USEPA, 2000c; USEPA, 2000d). The NDWAC approved the Working Group's
recommendations in November 2000 and formally provided them to EPA in
December 2000 (NDWAC, 2000). The NDWAC recommended that EPA's review
include consideration of five key elements, as appropriate: health
effects, analytical and treatment feasibility, implementation-related
issues, occurrence and exposure, and economic impacts. The NDWAC
suggested that the Agency conduct an initial screening review of each
NPDWR to identify potential candidates for an in-depth analysis. As
discussed in more detail in section IV of today's action, EPA has
followed the general protocol recommended by the NDWAC.
In addition to the November 1999 stakeholder meeting and
consultation with the NDWAC, EPA representatives have delivered
presentations at a variety of meetings held by other organizations,
including: two American Water Works Association (AWWA) Technical
Advisory Workgroup meetings, one held in February 2001 in Washington,
DC, and one held in February 2002 in San Diego, CA; a meeting held by
the Association of State Drinking Water Administrators (ASDWA) in March
2001 in Alexandria, VA; and the annual AWWA meeting held in Washington,
DC in June 2001. At each of these meetings, stakeholders were given the
opportunity to comment on the protocol by which EPA was planning to
perform the review of existing NPDWRs. EPA received valuable input from
stakeholders on the planned protocol.
B. How Does EPA Plan To Involve the Science Advisory Board (SAB)?
EPA plans to consult with the SAB Drinking Water Committee on
today's action. The Agency will request their review and comment on
whether the protocol EPA developed based on the NDWAC recommendations
was consistently applied and appropriately documented.
III. Regulations Included in the Six-Year Review
Table III-1 lists the pre-1997 NPDWRs covered by today's action and
the rulemaking by which they were originally promulgated. Table III-2
lists the NPDWRs not covered by today's action. These include the
remaining pre-1997 NPDWRs which are being or have already been reviewed
in separate actions and the NPDWRs promulgated after the 1996 SDWA
Amendments. The
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NPDWRs listed in Table III-2 will be included in the 2002-2008 review
round. Section V of today's action summarizes the results of the review
of 68 pre-1997 chemical NPDWRs and the NPDWR for total coliforms.
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IV. EPA's Protocol for Reviewing the NPDWRs Included in Today's
Action
A. What Was EPA's Review Process?
The document, ``EPA Protocol for the Review of Existing National
Primary Drinking Water Regulations'' (USEPA, 2002f), contains a
detailed description of the process the Agency used to review the 69
NPDWRs discussed in today's action. EPA's primary goal was to identify
and prioritize candidates for regulatory revision in order to target
those revisions that are most likely to result in an increased level of
public health protection and/or result in substantial cost savings
while maintaining the level of public health protection. This section
provides an overview of the review process. Sections IV.B and IV.C of
today's action provide a more detailed description of how EPA applied
the process to the review of 68 chemical NPDWRs and the TCR,
respectively.
EPA applied the following basic principles to the review process:
Health effects, analytical feasibility, treatment data,
and analyses underlying existing regulations remain adequate and
relevant, except in those instances where reliable, peer-reviewed, new
data are available that indicate a need to re-evaluate an NPDWR (e.g.,
where a change in health risk assessment has occurred).
If new data were available, EPA determined whether changes
in existing standards were warranted. For example, in determining
whether there was a change in analytical feasibility, the Agency
applied the current policy and procedures for calculating the practical
quantitation level for drinking water contaminants.\1\
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\1\ See: 50 FR 46880, November 13, 1985 (USEPA, 1985); 52 FR
25690, July 8, 1987 (USEPA, 1987); 54 FR 22062, May 22, 1989 (USEPA,
1989a).
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EPA was unable to complete evaluation of certain new data
within the time available for the review. For example, if a new health
risk assessment for a contaminant was not completed during the review
cycle, EPA generally made a ``not revise'' decision on the rationale
that it was not appropriate to revise the regulation while the
assessment was ongoing. When an updated assessment is completed, EPA
will review the update and any new conclusions or additional
information associated with the contaminant during the next review
cycle. The Agency may make a determination to revise a particular NPDWR
before August 2008 where justified by new public health risk
information.
During the review, EPA identified areas where information
is inadequate or unavailable (data gaps) and is needed before an NPDWR
may be considered as a candidate for revision. Where the Agency has
been unable to fill such gaps during the review process, today's action
provides information about the data gaps so that further research and
data collection can be considered as part of the second review cycle.
For example, the review may identify a need to better understand new
treatment technologies. Such an information gap will need to be
considered in the context of EPA's overall OGWDW research strategy.
During the review process, the Agency did not consider
potential regulatory revisions that were already the subject of other
rulemaking activities.
EPA applied the Agency's peer review policy (USEPA,
2000i), where appropriate, to any new analyses.
Figure 1 provides an overview of the review process. To most
efficiently utilize limited resources and assure
[[Page 19038]]
continued public health protection, the Agency conducted the review in
two phases: (1) an initial technical review of all 69 NPDWRs discussed
in today's action; and (2) an in-depth technical evaluation of those
NPDWRs identified during the initial review as potential candidates for
revision.
1. Initial Technical Review
The initial review phase included these three screening and general
evaluation steps:
Health effects review. Identify NPDWRs for which the
Agency has revised health risk assessments that indicate possible
changes to the maximum contaminant level goal (MCLG) and perhaps to the
maximum contaminant level (MCL);
Current technology review. Identify NPDWRs where
improvements in analytical measurement or treatment feasibility might
allow the MCL to be established closer to the MCLG, or where
adjustments in treatment technique (TT) requirements might be
appropriate; and/or
Other regulatory revisions review. Identify NPDWRs where
adjustments to system monitoring and reporting requirements might be
appropriate and where such changes are not already being considered as
a part of another activity.
EPA generally determined that an NPDWR was not a candidate for
revision after the initial review if a health risk assessment was in
process or was initiated as a result of the review, since the Agency
does not believe it is appropriate to revise the NPDWR while a health
risk assessment is underway. The Agency also determined that an NPDWR
was not a candidate for revision after the initial screening if none of
the initial screening analyses identified a health or technological
basis for a regulatory revision.
2. In-Depth Technical Review
The Agency subjected the remaining NPDWRs to more in-depth
technical analyses. If the initial review indicated a possible revision
to the MCLG/MCL, EPA further considered health and technology factors
that might affect the development of a revised MCLG/MCL or revised
MCLG/TT requirements. The Agency also estimated potential occurrence
and exposure at PWSs at concentrations of regulatory interest for the
chemical NPDWRs and conducted a qualitative evaluation of economic
impacts. EPA based the qualitative economic evaluation primarily on
available occurrence and exposure data, to determine whether the
possible revision was likely to present an opportunity for significant
gains in public health protection and/or significant cost savings that
could be realized without lessening the level of public health
protection.
In the case of three contaminants, EPA identified data gaps that
could not be filled during the current review cycle. Figure 1 shows the
identification of data gaps as the final step in the review; however,
in some instances, data gaps were identified during earlier steps in
the process. Where this occurred, EPA did not conduct some or all of
the remaining analyses. If the Agency identified data gaps, EPA
determined not to revise the NPDWR.
After completing these comprehensive analyses, EPA identified those
NPDWRs that remain appropriate at this time, and those NPDWRs that may
be appropriate for revision.
Today's action discusses the Agency's preliminary determinations
and seeks public comment on them. After considering the public comments
received and any new peer-reviewed data that may become available to
the Agency, EPA will publish its final decision in the FR.
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B. How Did EPA Review the Chemical NPDWRs?
This section describes the specific technical reviews that EPA
conducted for the chemical NPDWRs.
1. Health Effects
The document, ``Six-Year Review--Chemical Contaminants--Health
Effects Technical Support Document'' (USEPA, 2002i), describes how EPA
reviewed the chemical contaminants discussed in today's action and
provides the results of the health effects technical review. The
principal objective of the health effects review was to identify each
contaminant for which a new health risk assessment indicated that a
change in MCLG might be appropriate. For most of
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the chemical NPDWRs discussed in today's action, the MCLG is derived
from the cancer classification and/or the reference dose (RfD), as
described in Appendix A. Therefore, the health effects technical review
focused on whether there has been a change to these values. The Agency
reviewed the results of health risk assessments completed under the
following programs to determine if there had been a change in critical
effect or dose-response pattern that indicates the possible need for an
MCLG revision.
EPA Integrated Risk Information System (IRIS);
EPA Office of Pesticide Programs (OPP);
Agency for Toxic Substances and Disease Registry (ATSDR);
and
National Academy of Sciences (NAS).
Table IV-1 reflects the outcome of the health effects review for
the 68 chemical NPDWRs discussed in today's action. EPA placed each
contaminant into one of the following categories.
New risk assessment 1997 or later. An IRIS, OPP, ATSDR,
and/or NAS assessment has been completed in 1997 or later. These
assessments have considered developmental and reproductive toxicity as
a part of the assessment. The Agency considers these assessments to be
recent enough that it is not necessary to conduct a literature search
to identify any additional relevant studies that have become available
on the toxicological effects of these contaminants. In cases where the
health risk assessment resulted in a change in the critical effect, or
the dose-response pattern for a regulated contaminant, and where that
change could result in a change in the MCLG, EPA subjected the NPDWR to
more in-depth analysis as a part of the review process. Where recent
assessments were conducted by an agency other than EPA and new
developmental and reproductive data were identified, EPA initiated an
update of its assessment.
New risk assessment since promulgation, but prior to 1997.
An IRIS, OPP, ATSDR, and/or NAS assessment has been completed since the
NPDWR was promulgated but prior to 1997. None of these assessments
reflected a change in RfD or cancer classification. However, since
these assessments may not have specifically considered developmental
and reproductive health effects, EPA conducted a full literature
search, including developmental and reproductive toxicity, for those
NPDWRs with non-zero MCLGs to identify any relevant studies that might
affect the MCLGs of these contaminants. EPA did not identify any
chemicals for which developmental or reproductive effects might now be
the critical effect.\2\
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\2\ A zero MCLG is already considered protective of public
health and new information on developmental and reproductive effects
would not affect the MCLG. However, for those NPDWRs with a zero
MCLG, EPA reviewed available information to inquire whether data
show a nonlinearity of the dose-response; EPA did not find any data
to support such a mode of action (USEPA, 2002i).
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Agency risk assessment in process and not completed as of
February 2002. The Agency currently is conducting a health risk
assessment for the contaminant. That assessment will consider all
relevant studies that have become available on the toxicology of the
contaminant, including developmental and reproductive toxicity. EPA
does not believe it is appropriate to revise the MCLG for these
contaminants at this time.
Original NPDWR risk assessment. No health risk assessment
has been conducted since promulgation of the NPDWR. The Agency
conducted a full toxicological literature search, including
developmental and reproductive toxicity, for each of these contaminants
with non-zero MCLGs (see footnote 2) to identify new toxicological
studies that might have an impact on the MCLGs. In a few instances, the
results of the literature search indicate that it might be appropriate
to revise the RfD and/or cancer classification. EPA initiated updates
to the risk assessments for these chemicals, and established a schedule
for their completion. EPA does not believe it is appropriate to revise
the MCLG at this time.
Thus, only contaminants in the first category might be potential
candidates for an MCLG revision at this time.
The initial health effects review identified beryllium, oxamyl, and
picloram as potential candidates for an MCLG revision, depending on the
outcome of the more in-depth health effects review and on the other
technical analyses (e.g., analytical feasibility, treatment,
occurrence, etc.). The initial health effects review also identified
changes in the RfD for chromium as well as data gaps with respect to
its potential carcinogenicity via oral ingestion. EPA also identified
health effects-related data gaps for fluoride. Contaminants in any of
the categories except the third (risk assessment in process) may be
candidates for a new assessment if the initial health effects review
identified new studies that may affect the contaminant's RfD or cancer
classification. EPA has initiated a new assessment for cyanide, di(2-
ethylhexyl)adipate, and thallium as a result of the health effects
technical review.
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2. Analytical Feasibility
Since EPA has a process in place to approve new analytical methods
for drinking water contaminants, the actual review and approval of
potential new methods are outside the scope of the Six-Year Review
protocol. EPA recognizes that the approval and addition of new and/or
improved analytical methods (since the promulgation of the NPDWRs under
this review) may enhance the ability of laboratories to quantify
contaminants at lower levels. For this reason, EPA evaluated whether
there have been changes in analytical feasibility for a subset of the
68 chemical NPDWRs discussed in today's action. The document,
``Analytical Feasibility Support Document for the Six-Year
[[Page 19042]]
Review of Existing National Primary Drinking Water Regulations
(Reassessment of Feasibility for Chemical Contaminants)'' (USEPA,
2002d), describes the process EPA used to evaluate possible changes in
analytical feasibility and provides the results of the analytical
feasibility analyses. The purpose of these analyses is to determine
whether changes in the practical quantitation level (PQL) are possible
in those instances where the MCL is limited, or might be limited, by
analytical feasibility. EPA uses the PQL to estimate the level at which
laboratories can routinely measure a chemical contaminant in drinking
water. Historically, EPA has used two main approaches to determine a
PQL for SDWA analytes: (1) data from water supply (WS) studies, the
preferred alternative when sufficient WS data are available; or (2) a
multiplier method, in which the PQL is calculated by multiplying the
EPA-derived method detection limit (MDL) by a factor of 5 or 10 (50 FR
46880, November 13, 1985 (USEPA, 1985); 52 FR 25690, July 8, 1987
(USEPA, 1987); 54 FR 22062, May 22, 1989 (USEPA, 1989a)).
EPA performed the analytical feasibility analyses under two
circumstances. First, for those contaminants where the MCL is currently
limited by analytical feasibility (i.e., the MCL is set at the PQL) and
the MCLG is still appropriate, EPA evaluated the currently approved
methods for those contaminants and available WS data to determine
whether it might be possible to lower the PQL and hence set an MCL that
is closer to the MCLG. Section V of today's action provides the results
of the analytical feasibility review of 11 contaminants that are not
currently undergoing a health risk assessment and for which the MCL was
limited by analytical feasibility. These 11 contaminants include 10
with zero MCLGs \3\ and 1 with a non-zero MCLG. Of these 11, EPA
identified 10 where the data indicate it might be possible to set a
lower PQL (see Table IV-2). Although the data are indicative of a lower
PQL for these 10, they are not definitive and considered to be
insufficient to support an actual recalculation at this time. To
determine whether it was worthwhile to gather more definitive data for
PQL recalculation, EPA estimated what the potentially lower PQL could
be for these 10 analytes and used these values in the occurrence and
exposure analyses.\4\ As discussed for specific contaminants in section
V of today's action, EPA believes that a negligible gain in public
health exists at the possibly lower PQL for 9 of these 10 NPDWRs. The
results of the occurrence and exposure analysis for dichloromethane,
using the possibly lower PQL as a concentration value, indicate that it
may be appropriate to consider gathering data to recalculate a more
definitive PQL for this analyte.
---------------------------------------------------------------------------
\3\ Although they have a zero MCLG, EPA excluded lead and
epichlorohydrin from the analytical feasibility review since they
are TT rules and do not have an MCL.
\4\ Using WS data to derive the PQL for chemical NPDWRs involves
determining the concentration of an analyte at which 75 percent of
EPA Regional and State laboratories achieve results within a
specified acceptance window (see 54 FR 22062 at 22100, May 22, 1989
(USEPA, 1989a)). In re-evaluating more recent WS data for the Six-
Year Review, sufficient data were not available around the 75
percent critierion to actually recalculate the PQL. However, if the
passing rates for the EPA Regional and State laboratories exceeded
80 to 85 percent at spike concentrations close to the current PQL,
this information was considered to be indicative of a possible
change in the PQL. If data indicated a possible change in the PQL,
EPA then evaluated the distribution of the analytical methods used
to analyze the spike samples in the WS studies. Evaluation of the
method usage over time allowed EPA to determine the analytical
methods that appear to be the most widely used for the analysis of a
particular contaminants. Knowledge of which analytical methods are
the most widely used, along with the MDL for these methods, and a 10
times MDL multiplier allowed EPA to estimate where the potential
lower limit of quantitation may lie today. This estimated PQL was
used as a value in the occurrence analysis to help the Agency
determine if there may be a significant gain in public health
protection if EPA were to consider gathering the information needed
to recalculate the PQL.
---------------------------------------------------------------------------
The second circumstance under which EPA re-evaluated the PQL was
for three of the four contaminants identified under the health effects
technical review as potential candidates for revision (see Table IV-2).
These three contaminants were evaluated to determine if any potential
MCL revision would be limited by analytical feasibility. Based on this
review, EPA believes that analytical feasibility may be a limiting
factor for revising the MCL for oxamyl (see section V.A.50 of today's
action for a more detailed discussion). The Agency believes that
analytical feasibility would not be a limiting factor for the remaining
two contaminants identified by the health effects review as having
potential changes in their MCLG (i.e., beryllium and chromium).
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3. Treatment Feasibility
An NPDWR either identifies the Best Available Technology (BAT) for
meeting an MCL, or establishes enforceable treatment technique (TT)
requirements. Currently, for all the chemical NPDWRs covered in today's
action that include an MCL, the MCL is set equal to either the MCLG or
the PQL. None of these MCLs are currently limited by treatment
feasibility. Thus, as a part of the Six-Year Review process, EPA only
needed to review available information on treatment technologies if
either of the following conditions applied:
The health effects technical review identified a potential
change to the MCLG/MCL (applied to 4 NPDWRs); or
A health risk assessment is not in process for the
contaminant and one of the following two conditions apply:
(1) the analytical feasibility review identified a possible change
to the PQL and thus to the MCL (applied to 10 NPDWRs); or
(2) the NPDWR is a TT-type rule (applied to 3 NPDWRs).
The draft EPA document, ``Water Treatment Technology Feasibility
Support Document for Chemical Contaminants; In Support of EPA Six-Year
Review of National Primary Drinking Water Regulations'' (USEPA, 2002k),
describes the process EPA used to evaluate treatment feasibility, where
appropriate, for the chemical NPDWRs discussed in today's action and
provides the results of these analyses. As a part of this review, EPA
utilized the same sources that have been the primary resources in
development of EPA regulations and guidance, including published EPA
treatment reports, peer-reviewed journals, and other technology
sources, as well as information received from EPA stakeholders.
a. MCL-type Rules. EPA evaluated existing treatment technology
information for 14 MCL-type NPDWRs (see Table IV-3) to determine
whether treatment feasibility would be a limiting factor if EPA were to
lower the MCL. In addition and where appropriate, EPA evaluated the
likelihood that systems would discontinue existing treatment if EPA
were to raise the MCL.
Based upon this preliminary evaluation, the Agency believes that
treatment capabilities would be adequate to support a lower MCL value,
if EPA were to revise the MCL for any of the contaminants for which a
lower MCL may be appropriate (USEPA, 2002k). Treatment technologies
specified as BAT within the current NPDWR, and small system compliance
technologies which were specified by EPA in 1998 (USEPA, 1998a) are
considered to be efficient and practical for implementation at PWSs.
However, if EPA were to determine that it is appropriate to revise any
of these NPDWRs, it would undertake a more thorough review of treatment
feasibility, including a consideration of costs, to
[[Page 19044]]
determine whether treatment feasibility would be a constraint or not.
In a few instances, the Agency identified some potential treatment
effectiveness research needs that will be considered in the context of
the overall drinking water research strategy.\5\ The revise/not revise
decisions discussed in section V of today's action do not depend on EPA
addressing these research needs.
---------------------------------------------------------------------------
\5\ Refer to the document, ``Water Treatment Technology
Feasibility Support Document for Chemical Contaminants; In Support
of EPA Six-Year Review of National Primary Drinking Water
Regulations'' (USEPA, 2002k) for a description of these research
needs.
---------------------------------------------------------------------------
In two instances (beryllium \6\ and picloram), the outcome of the
health effects technical review indicated it might be appropriate to
raise the MCLG/MCL. For these two contaminants, BATs specified in the
NPDWR are also BATs for several other contaminants (USEPA, 2002k).
Available data are insufficient for EPA to determine how many PWSs are
specifically treating for either of these contaminants using the same
treatment for co-occurring contaminants and/or for secondary benefits.
The Agency thus cannot determine whether these water systems would
discontinue existing treatment if the MCL were to be raised (USEPA,
2002c; USEPA, 2002k). However, in both cases, relatively few systems
would be affected so there would be little potential for significant
cost savings at a national level.
---------------------------------------------------------------------------
\6\ As discussed in section V.A.9.b of today's action, the
outcome of the health effects technical review indicates it might be
possible to either lower or raise the MCLG/MCL.
---------------------------------------------------------------------------
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b. Treatment Technique-type Rules. EPA reviewed three of the four
chemical NPDWRs for which a TT is set in lieu of an MCL (copper,
epichlorohydrin, and lead). A health risk assessment is in process for
the fourth TT-type NPDWR, acrylamide.
The Agency found no new information relating to new treatment or
other technology which would support a revision to the TT for
epichlorohydrin at this time. EPA also reviewed issues relating to
current TT requirements for copper and lead that were identified by EPA
and/or stakeholders. Sections V.A.15 and V.A.43 of today's action
summarize these issues for copper and lead, respectively. EPA believes
these TT requirements remain appropriate at this time; however, EPA has
identified a few potential treatment effectiveness research needs and
will consider them in the context of the overall drinking water
research strategy (USEPA, 2002k).
4. Other Regulatory Revisions
In addition to possible revisions to MCLGs, MCLs, and TTs, EPA
considered other regulatory revisions, such as monitoring and system
reporting requirements, as a part of the Six-Year Review process. EPA
focused this review on issues that are not already being addressed, or
have not been addressed, through alternative mechanisms (e.g., as part
of a recent or ongoing rulemaking, in conjunction with possible
chemical monitoring reform, etc.). Where appropriate alternative
mechanisms do not exist, EPA considered these implementation-related
concerns if the potential revision met the following criteria:
It indicated a potential change in the 40 Code of Federal
Regulations (CFR) 141 requirements;
It was ``ready'' for rulemaking--that is, the problem to
be resolved has been clearly identified and specific option(s) have
been formulated to address the problem; and
It met at least one of the following conditions:
--Clearly improved the level of public health protection; and/or
--Represented a significant cost savings while maintaining or improving
the public health protection.
The document, ``Consideration of Other Regulatory Revisions for
Chemical Contaminants in Support of the Six-Year Review of National
Primary Drinking Water Regulations'' (USEPA, 2002e) summarizes the
specific issues identified during the review process. Some of these
issues (e.g., the need to specifically define new system/new source
monitoring requirements for chemical contaminants) have already been
addressed in the recently published arsenic and radionuclides NPDWRs
(66 FR 6975, January 22, 2001 (USEPA, 2001a); 65 FR 76707, December 7,
2000 (USEPA, 2000g)). Additional issues are contaminant-specific, and
are discussed in conjunction with the review of the NPDWR in section V
of today's action.
5. Occurrence and Exposure Analysis
EPA's goal in evaluating contaminant occurrence was to estimate the
number of PWSs at which contaminants occur at levels of regulatory
interest in drinking water, and to evaluate the number of people
exposed to these levels. For its occurrence analysis, EPA used drinking
water compliance monitoring data from 16 States, collected in the 1993
to 1997 time frame, and statistically analyzed the data to estimate
occurrence. The
[[Page 19045]]
support document ``Occurrence Estimation Methodology and Occurrence
Findings Report for the Six-Year Regulatory Review'' describes in
detail the development of the data set and the statistical methodology
for analysis (USEPA, 2002g). This section presents a summary of the
data and analysis.
a. Development of the 16-State Contaminant Occurrence Data Set. For
the current Six-Year Review, EPA used PWS contaminant monitoring
results, voluntarily provided by 16 States, as the primary source of
information. EPA selected these States based on their geographic
diversity and on their agricultural and industrial pollution potential.
EPA also used data from a number of additional sources for comparative
purposes. These secondary sources include the Safe Drinking Water
Information System (SDWIS), the U.S. Geological Survey's National Water
Information System (NWIS), EPA's Unregulated Contaminant Information
System (URCIS), and other privately- and publicly-available data
sources (USEPA, 2002g). In future reviews rounds, EPA plans to use the
National Drinking Water Contaminant Occurrence Database (NCOD) as the
primary data source when conducting the occurrence and exposure
analyses as a part of the Six-Year Review process. EPA is in the
process of populating the NCOD, however, sufficient data from the NCOD
are not yet available.
EPA developed the 16-State contaminant occurrence data set in two
stages. In the first stage, EPA developed an 8-State cross-section to
support occurrence analyses for its Chemical Monitoring Reform (CMR)
evaluation. The Agency selected the eight States for use in a national
analysis because they provided the best data quality and completeness,
and formed a balanced national cross-section of occurrence data based
on the States' geographic distribution and relative rankings in
pollution potential, as described later in this section. The
methodology for selecting the State data sets is described in an EPA
report, ``A Review of Contaminant Occurrence in Public Water Systems''
(USEPA, 1999d). EPA had this report externally peer reviewed and also
received public comment from stakeholders. In the second stage, for the
current Six-Year Review, EPA augmented the data from the CMR 8-State
data set with data from 8 additional States. The resulting data set
includes 13 million analytical results, from approximately 41,000 PWSs
in 16 States. For the 14 contaminants that EPA identified for detailed
occurrence analysis, i.e., those with either new health effects
information or a potential change in the PQL (see Table IV-3 of today's
action), the number of analytical results per contaminant varies from
about 34,000 to greater than 200,000; the number of PWSs with data
varies from about 8,000 to 23,000; and the number of States providing
relevant data varies from 13 to 16.
All samples in the 16-State data set were standard SDWA compliance
samples. Data were limited to those with confirmed water source and
sampling type information. ``Special'' samples, ``investigation''
samples (investigating a contaminant problem, that would likely bias
the results), or samples of unknown type were excluded from further
analysis. EPA conducted various quality control and review checks of
the results, including follow-up questions to the States providing the
data to clarify potential reporting inconsistencies, records with
invalid codes, or use of analytical units. The Agency then compiled
State data sets into a single database with a unified format.
In selecting a cross-section of State data sets that is generally
representative of the U.S., EPA considered two broad factors:
geographic or spatial diversity, and pollution potential. Geographic
diversity in the data set helps to ensure that contaminant occurrence
data come from areas representing the range of climatic and hydrologic
conditions across the U.S. A range of agricultural and industrial
pollution potential helps to ensure that the data represent the range
of likely contaminant occurrence across the United States.
As indicators of States' pollution potential, EPA used two primary
measures: the number of manufacturing facilities per square mile (to
reflect the potential for VOC occurrence), and the total expenditures
on farm agricultural chemicals (to reflect the potential for synthetic
organic chemical (SOC) occurrence). In order to construct a cross-
section with a balance of pollution potential, EPA divided the 50
States into high and low pollution potential groups based on their rank
orderings with respect to the two primary pollution potential
indicators. For each of the two pollution potential indicators, EPA
ranked the 50 States from 1 to 50 (1 being the highest and 50 being the
lowest). The States were then plotted on a two-dimensional scatter plot
(see Figure 2), with the x- and y-axes representing the manufacturing
and agricultural ranking, respectively, of each State. The amount spent
on agricultural chemicals per State increases along the y-axis from
bottom to top. The number of manufacturing establishments per square
mile per State increases along the x-axis from left to right. EPA then
reviewed the rankings and selected a subset of 16 States (the ``cross-
section States'') in order to give approximate balance across the range
of pollution indicators.
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The bold cross in the center of Figure 2 separates the plot into
four quadrants. The upper right-hand quadrant contains the States with
the most manufacturing establishments per square mile and the greatest
amount of farm agricultural chemical expenses. These States, therefore,
have the greatest amount of pollution potential based on these
manufacturing and agricultural indicators. The lower left-hand quadrant
[[Page 19047]]
contains the States with the least amount of manufacturing
establishments per square mile and the least amount of farm
agricultural chemical expenses. This quadrant, therefore, contains the
States with the least amount of pollution potential, based on these
indicators. To identify the location of each of the 16 States within
the quadrants, find the intersection of the State name from the x- and
the y-axes. This intersection should be represented by either a filled-
in circle (one of the original 8 States), or a filled-in triangle (one
of the additional 8 States).
The Agency performed analyses to verify the validity of this
approach. The results of these analyses support the applicability of
these indicators relative to pollution potential. The mean
concentration values for select contaminants were estimated for groups
of top quartile and bottom quartile States. The cross-section
development approach presumes that the top quartile States have a
higher pollution potential than the bottom quartile States, and,
therefore, the estimated mean concentrations for the top quartile
States should be greater than those for the bottom quartile States. The
estimated mean concentration values for the top quartile States were
always higher than the mean concentration for the bottom quartile
States with the lone exception of heptachlor (a very low occurrence
SOC).
EPA believes the distribution of the 16 selected States is
representative of the national distribution of States with respect to
these pollution indicators. Eight of the selected States comprised
EPA's original 8-State cross-section that was used for the CMR
analyses; EPA solicited occurrence data from the remaining eight. The
geographic distribution of the resulting 16-State cross-section is
shown in Figure 3. Other, secondary pollution potential indicators were
also considered in order to help ensure that the data were
representative of the range of pollution potential across the U.S.
While this cross-section does not represent a statistical random
sample of States, and thus, does not capture all local variations in
occurrence, EPA, nonetheless, believes that the data set provides a
reliable picture of overall distribution of contaminant occurrence in
the U.S.
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b. Analysis of Contaminant Occurrence. Statistical analysis of
contaminant occurrence was focused at the water system level. The goal
was to estimate the fraction of PWSs with contaminant occurrence above
levels of regulatory interest, and the corresponding fraction of people
exposed to those levels.
Occurrence analysis proceeded in two stages. For the initial, or
``Stage 1'' analysis, EPA computed simple occurrence measures which are
more straightforward and conservative than a full probabilistic
analysis. In this stage of analysis, EPA estimated the percent of PWSs
and total population served by PWSs with at least one analytical result
exceeding concentrations equal to specified contaminant levels. EPA
considered three specified contaminant levels: The lower limit of
detection reported by the States, one-half the current MCL, and the
current MCL. Of the 68 chemicals discussed in today's
[[Page 19048]]
action, 60 were analyzed in this way. The exceptions were:
The two contaminants for which not enough data were
available (dioxin and asbestos);
The four contaminants for which the NPDWR specifies a TT-
type requirement instead of an MCL (acrylamide, copper,
epichlorohydrin, and lead); and
The two contaminants for which EPA did not request data,
since the Agency determined there was no health or technological basis
for revising, and because these data would have required extra effort
for States to transmit (nitrate and nitrite).
Because of the simple and conservative nature of Stage 1 estimates, EPA
used them only as preliminary indicators of contaminant occurrence, to
guide further analysis. The occurrence support document (USEPA, 2002g)
includes the details of the Stage 1 analyses.
Following the initial occurrence analysis, EPA performed a more
detailed, ``Stage 2'' statistical analysis of occurrence for the 14
contaminants identified as potential candidates by the health effects
and analytical feasibility technical reviews. This analysis used a
statistical model, known as a Bayesian hierarchical model, to estimate
the number of systems (and the corresponding affected populations) with
mean contaminant concentrations above the levels of regulatory
interest. Statistical modeling is usually required in order to estimate
mean contaminant concentrations, because many sample concentrations are
non-detects, meaning that the true concentration is unknown and may
range anywhere from zero to the detection limit of the analytical
method. In the hierarchical model, individual samples are assumed to be
log-normally distributed within entry points to a distribution system
(EPTDS) (e.g., wells or treatment plants); EPTDS means are assumed to
be log-normally distributed within each water system; and system means
are assumed to be log-normally distributed nationwide. This model can
be applied to estimate the number of systems with mean concentrations
above levels of interest, and also the amount of variability between
sources within a system. Population exposure can also be estimated at
the same time, by using information from EPA's SDWIS database about the
population served by each system in the database. The hierarchical
model has important advantages:
It provides a unified model for estimating occurrence,
both between and within systems;
It uses information about non-detected concentrations; and
It provides uncertainty intervals around each estimate,
taking into account both sampling variability over time and across
systems, and uncertainty due to non-detected concentrations.
Details of the hierarchical model, and its application to
estimating mean contaminant concentrations, are provided in the
occurrence support document (USEPA, 2002g).
The results of the Stage 2 analyses for each of the 14 contaminants
listed in Table IV-3 are presented in section V.A of today's action.
These results represent only the systems in EPA's 16-State database.
EPA considered this the most straightforward and accurate way to
present the data that were available for the review process. As
indicated in the preceding discussion of the development of the
analysis of contaminant occurrence, EPA developed the more refined
Stage 2 analysis based on the preliminary evaluation using the results
of the Stage 1 analysis. A detailed explanation of this process is
provided in EPA's occurrence support document and is available for
review and comment (USEPA, 2002g).
For those contaminants where occurrence was evaluated with respect
to the revise/not revise decision, EPA used the Stage 2 occurrence
analysis for the 16 States to determine the percentage of PWSs that
could be impacted, and the percentage of the exposed population served
by these systems. Section V contains a discussion of the incremental
percentage of systems and the incremental percentage of the population
served by these systems. That is, EPA considered the difference between
levels of occurrence and exposure above the current MCL and the
occurrence and exposure at the potentially revised level(s).
6. Economic Considerations
While SDWA provides the Agency with broad discretion to consider
economics in the context of the Six-Year Review, the statute precludes
EPA from using economics as the sole basis for a revision that would
provide less health protection than the current standard (i.e., anti-
backsliding). However, if new peer-reviewed scientific health effects
research indicates that an MCLG could be raised while maintaining
public health protection, then such a change is permitted. For NPDWRs
published after the 1996 SDWA Amendments, Congress added specific
requirements for economic and cost-benefit analyses in their
development. Where EPA decides to revise an NPDWR based on health
effects or other technical reasons, economic factors, including
feasibility and an assessment of costs and benefits in accordance with
Section 1412(b)(6) of the SDWA, must then be taken into consideration.
EPA considered likely economic impacts, based primarily on available
occurrence and exposure data, to qualitatively evaluate whether the
potential revisions identified by the health and technology reviews may
present a significant opportunity for improved or strengthened public
health standards and/or a significant cost savings while maintaining
public health protection (USEPA, 2002c).
C. How Is EPA Reviewing the Total Coliform Rule?
The memorandum, ``Six-Year Review of the Total Coliform Rule--
Comments Received'' (USEPA, 2002j), describes the process EPA applied
to the review of the TCR. Where appropriate, EPA applied the same
approach to reviewing the TCR as it did to the review of the chemical
NPDWRs discussed in today's action. However, because of the nature of
the TCR and the pathogens it controls, the Agency focused its review on
the implementation-related requirements. As discussed in section V.B of
today's action, these analyses indicate that a rulemaking to initiate
possible revisions to the TCR is appropriate at this time.
D. How Did EPA Factor Children's Health Concerns Into the Review?
The 1996 amendments to SDWA require special consideration of all
sensitive populations (infants, children, pregnant women, elderly, and
immunocompromised) in the development of drinking water regulations
(Section 1412(b)(3)(C)(V) of SDWA, as amended in 1996). Over the past
decade, the amount of available data on the impact of chemical
contaminants on conception and early developmental life stages has
increased dramatically. Accordingly, as a part of the Six-Year Review
process, EPA completed a literature search covering developmental and
reproductive endpoints (fertility, embryo survival, developmental
delays, birth defects, endocrine effects, etc.) for regulated chemicals
that have a non-zero MCLG and have not been the subject of an updated
1997 or later risk assessment (see section IV.B.1 of today's action).
EPA reviewed the output from the literature searches to identify any
studies that might have an influence on the present MCLG. Three
chemicals were identified with potential developmental/reproductive
endpoints of concern: cyanide, di(2-ethylhexyl)adipate (DEHA), and
[[Page 19049]]
thallium (see sections V.A.16, V.A.28, and V.A.59 of today's action).
In each case, where the literature search indicated a need to consider
recent studies of developmental or reproductive toxicity, EPA has
initiated the process to update the Agency risk assessment. Assessments
conducted by EPA, ATSDR, and NAS in 1997 or later thoroughly considered
the potential for reproductive and developmental toxicity; thus,
literature searches for chemicals with such recent assessments were not
necessary.
Young children, especially infants, are generally at greater health
risk from infections caused by waterborne pathogens. Any revision to
the TCR will maintain or improve the control of waterborne pathogens
and, therefore, the protection afforded to children.
V. EPA's Preliminary Decisions Based on its Review of NPDWRs
Included in Today's Action
Table V-1 lists EPA's preliminary revise/not revise decision for
each of the 69 NPDWRs discussed in today's action along with the
principal rationale for the decision. If EPA has decided it is not
appropriate to revise an NPDWR at this time, that decision is based on
one of the following reasons.
Health risk assessment is in process: The Agency is
currently conducting, or has scheduled, a detailed review of current
health effects information. Because the results of the assessment are
not yet available, the Agency does not believe it is appropriate to
make a ``revise decision'' at this time. In these cases, today's action
does not include a discussion of the review of other key elements
(e.g., technology, ``other regulatory revisions'', and occurrence/
exposure analyses). EPA will consider the results of the updated health
risk assessment during the 2002-2008 review cycle. However, if the
results of the health risk assessment indicate a compelling need to
reconsider the MCLG, EPA may decide to accelerate the review schedule
for that contaminant's NPDWR.
NPDWR remains appropriate after data/information review:
The outcome of the review indicates that the current regulatory
requirements remain appropriate and, therefore, no regulatory revisions
are warranted. Any new information available to the Agency either
supports the current regulatory requirements or does not justify a
revision.
New information, but no revision recommended because:
--Negligible gain in public health protection: Any resulting
changes to the NPDWR would not significantly improve the level of
public health protection or result in a major cost savings.
--Information Gaps: Although results of the review support
consideration of a possible revision, the available data are
insufficient to support a definitive regulatory decision at this time.
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A. What Preliminary Decisions Has EPA Made Regarding the Chemical
NPDWRs?
1. Acrylamide
a. Background. EPA published the current NPDWR for acrylamide on
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an
MCLG of zero based on a cancer classification of B2, probable human
carcinogen. The NPDWR imposes a TT requirement that limits the
allowable monomer levels in products used during drinking water
treatment, storage, and distribution to 0.05 percent acrylamide in
polyacrylamide coagulant aids dosed at 1 part per million (ppm). Each
water system is required to certify, in writing, to the State (using
third-party or manufacturer's certification) that the product used
meets these residual monomers and use-level specifications.
b. Technical Reviews. EPA has initiated a reassessment of the
health risks resulting from exposure to acrylamide. The revised risk
assessment will consider relevant studies that have become available on
the toxicity of
[[Page 19051]]
acrylamide including its potential developmental and reproductive
toxicity. The Agency expects the new risk assessment to be completed in
the 2004 or 2005 time frame (USEPA, 2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for acrylamide is appropriate at this time because a
reassessment of the health risks resulting from exposure to acrylamide
is ongoing.
2. Alachlor
a. Background. EPA published the current NPDWR for alachlor on
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an
MCLG of zero based on a cancer classification of B2, probable human
carcinogen. The NPDWR also established an MCL of 0.002 milligrams per
liter (mg/L) based on analytical feasibility.
b. Technical Reviews. The Agency updated the health risk assessment
for alachlor in 1998 as a part of the pesticides reregistration process
(USEPA, 2002i). However, the Agency has initiated another update to the
alachlor health risk assessment. The revised risk assessment will
consider relevant studies that have become available on the toxicity of
alachlor including its potential developmental and reproductive
toxicity. The Agency expects the new risk assessment to be completed in
the 2002 or 2003 time frame.
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for alachlor is appropriate at this time because a
reassessment of the health risks resulting from exposure to alachlor is
ongoing.
3. Antimony
a. Background. EPA published the current NPDWR for antimony on July
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG and
an MCL of 0.006 mg/L. EPA based the MCLG on an RfD of 0.0004 milligrams
per kilogram of body weight per day (mg/kg/day) and a cancer
classification of D, not classifiable as to human carcinogenicity.
b. Technical Reviews. EPA has initiated a reassessment of the
health risks resulting from exposure to antimony. The revised risk
assessment will consider relevant studies that have become available on
the toxicity of antimony including its potential developmental and
reproductive toxicity. The Agency expects the new risk assessment to be
completed in the 2002 or 2003 time frame (USEPA, 2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for antimony is appropriate at this time because a
reassessment of the health risks resulting from exposure to antimony is
ongoing.
4. Asbestos
a. Background. EPA published the current NPDWR for asbestos on
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an
MCLG and an MCL of 7 million fibers per liter (MFL) for asbestos fibers
exceeding 10 micrometers in length. EPA evaluated asbestos as a
Category II \7\ contaminant (equivalent to Group C, possible human
carcinogen) by the oral route of exposure (see Appendix A of today's
action for discussion of cancer classifications).
---------------------------------------------------------------------------
\7\ Category II contaminants include those contaminants for
which EPA has determined there is limited evidence of
carcinogenicity from drinking water considering weight of evidence,
pharmacokinetics, potency, and exposure. For Category II
contaminants, EPA has used two approaches to set the MCLG: Either
(1) setting the MCLG based upon noncarcinogenic endpoints of
toxicity (the RfD) then applying an additional risk management
factor of 1 to 10; or (2) setting the MCLG based upon a theoretical
lifetime excess cancer risk range of 10-\5\ to
10-\6\ using a conservative mathematical extrapolation
model.
---------------------------------------------------------------------------
b. Technical Reviews. EPA has initiated a reassessment of the
health risks resulting from exposure to asbestos. The new risk
assessment will consider relevant studies that have become available on
the toxicity of asbestos, including its potential developmental and
reproductive toxicity. The Agency expects the new risk assessment to be
completed in the 2004 or 2005 time frame (USEPA, 2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for asbestos is appropriate at this time because a
reassessment of the health risks resulting from exposure to asbestos is
ongoing.
5. Atrazine
a. Background. EPA published the current NPDWR for atrazine on
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an
MCLG and an MCL of 0.003 mg/L. EPA based the MCLG on an RfD of 0.005
mg/kg/day and a cancer classification of Group C, possible human
carcinogen, based on limited evidence of carcinogenicity in animals in
the absence of human data. EPA published an FR notice in February 1999,
in which EPA responded to recommendations by the Children's Health
Advisory Committee, by committing to re-evaluate the MCL for atrazine
after the Agency has finalized its risk assessment (64 FR 5277,
February 3, 1999 (USEPA, 1999a)).
b. Technical Reviews. EPA has initiated a reassessment of the
health risks resulting from exposure to atrazine. The revised risk
assessment will consider relevant studies that have become available on
the toxicity of atrazine including its potential developmental and
neuroendocrine effects. The Agency expects the new risk assessment to
be completed in the 2002 time frame. EPA is in the process of
conducting an occurrence and exposure analysis.
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for atrazine is appropriate at this time because a
reassessment of the health risks resulting from exposure to atrazine is
ongoing. EPA has committed to revisiting the NPDWR for atrazine if a
revision is appropriate once the results of the revised risk assessment
become available. Therefore, EPA will revisit this ``not revise''
decision once the new risk assessment is completed.
6. Barium
a. Background. EPA published the current NPDWR for barium on July
1, 1991 (56 FR 30266 (USEPA, 1991c)). The NPDWR established an MCLG and
an MCL of 2 mg/L. EPA based the MCLG on an RfD of 0.07 mg/kg/day and a
cancer classification of D, not classifiable as to human
carcinogenicity.
b. Technical Reviews. The Agency updated the health risk assessment
for barium in 1998 and retained the RfD and cancer classification on
which the 1991 MCLG is based (USEPA, 1999f). As a part of the 1998
assessment, EPA considered all relevant data on the toxicity of barium
including developmental and reproductive toxicity.
A review of analytical or treatment feasibility is not necessary
for barium because changes to the MCLG are not warranted at this time
and the current MCL is set at the MCLG. In addition, the results of
EPA's review of possible ``other regulatory revisions'' did not
identify any barium-specific issues (USEPA, 2002e). Since EPA did not
identify a health or technology basis for revising the barium NPDWR,
the Agency did not conduct a detailed occurrence and exposure analysis.
c. Preliminary Decision. After reviewing the results of the
pertinent technical analyses, the Agency believes the NPDWR for barium
remains appropriate and thus, it is not subject to revision at this
time.
[[Page 19052]]
7. Benzene
a. Background. EPA published the current NPDWR for benzene on July
8, 1987 (52 FR 25690 (USEPA, 1987)). The NPDWR established an MCLG of
zero based on a cancer classification of A, known human carcinogen. The
NPDWR also established an MCL of 0.005 mg/L based on analytical
feasibility.
b. Technical Reviews. The Agency updated the health risk assessment
for benzene in 2000 and retained the cancer classification on which the
1987 zero MCLG is based (USEPA, 2000j; USEPA, 2002i). The revised risk
assessment considered relevant studies on the toxicity of benzene
including developmental and reproductive toxicity.
The current MCL for benzene is based on a PQL of 0.005 mg/L. As a
part of the Six-Year Review, EPA analyzed more recent WS data to
determine if it might be possible to recalculate the PQL (USEPA,
2002d). In addition, the Agency evaluated whether more sensitive
analytical methods have been approved and put into use by a wide number
of laboratories. The analysis of the WS data indicates that an
improvement in analytical feasibility might exist. Evaluation of the WS
data shows that EPA Regional and State laboratories exhibit greater
than 95 percent laboratory passing rates at concentrations around the
current PQL of 0.005 mg/L. Because most of the laboratory passing rates
exceeded the 75 percent criterion typically used to derive a PQL from
WS studies, this information indicates that a lower PQL corresponding
to the 75 percent passing rate might exist for benzene. While this
information is indicative of a possibly lower PQL, the WS data are
insufficient at this time to actually recalculate what the lower PQL
for benzene might be.
Using information about the analytical methods most widely used to
report results in the WS studies, the MDLs for these methods, and the
10 times MDL multiplier, EPA estimated what the possibly lower PQL/MCL
might be. For the analysis of benzene in the more recent WS studies,
laboratories predominantly used EPA Method 524.2 (Gas Chromatography/
Mass Spectrometry or GC/MS), which has an upper limit MDL of 0.00004
mg/L. A 10 times MDL multiplier predicts that the PQL could lie around
0.0004 mg/L. The 0.0004 mg/L value is used as a threshold in the
occurrence analysis, which is discussed in this section.
Since the analytical feasibility analysis indicates that the PQL
for benzene (and therefore the MCL) could possibly be lower if EPA had
more definitive data to recalculate the PQL, EPA considered whether
treatment feasibility is likely to pose any limitations (USEPA, 2002k).
The current BATs for benzene are packed tower aeration (PTA) and
granular activated carbon (GAC). Small system compliance technologies
for benzene include GAC and several aeration technologies. EPA believes
these BATs are still practical and would not pose any limitations for
benzene at a possibly lower MCL.
The results of EPA's review of possible ``other regulatory
revisions'' did not identify any benzene-specific issues (USEPA,
2002e).
EPA evaluated the results of the occurrence and exposure analyses
for benzene to determine whether changes to the MCL might be
appropriate and likely to result in additional public health protection
if the PQL were recalculated (USEPA, 2002g; USEPA 2002h). Table V-2
shows the results of the detailed occurrence and exposure analysis
based on the 16-State cross-section for the current MCL (0.005 mg/L)
and the possible PQL/MCL based on the analytical feasibility analysis
(0.0004 mg/L).
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The results of the detailed occurrence and exposure analysis
indicate that approximately 0.3 percent of the 23,266 systems sampled
in the 16 cross-section States and approximately 0.3 percent of the
population served by those systems, might be affected if EPA were to
gather information to recalculate the PQL (to a lower PQL of around
0.0004 mg/L) and revise the MCL accordingly.
c. Preliminary Decision. Although there are new data that support
consideration of a possibly lower PQL (and therefore a possibly lower
MCL), EPA does not believe a revision to the NPDWR for benzene is
appropriate at this time. The Agency does not have sufficient data at
this time on which to base a PQL recalculation and hence an MCL
revision. In addition, because the occurrence of benzene appears to be
minimal between the current MCL and any likely PQL/MCL revision, the
Agency believes that any potential revisions to the benzene NPDWR are
unlikely to significantly improve the level of public health
protection.
8. Benzo[a]pyrene
a. Background. EPA published the current NPDWR for benzo[a]pyrene
on July 17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an
MCLG of zero based on a cancer classification of B2, probable human
carcinogen. The NPDWR also established an MCL of 0.0002 mg/L based on
analytical method feasibility.
b. Technical Reviews. EPA has initiated a reassessment of the
health risks resulting from exposure to benzo[a]pyrene. The revised
risk assessment will consider relevant studies that have become
available on the toxicity of benzo[a]pyrene including its potential
developmental and reproductive toxicity. The Agency expects the new
risk assessment to be completed in the 2002 or 2003 time frame (USEPA,
2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for benzo[a]pyrene is appropriate at this time because a
reassessment of the health risks resulting from exposure to
benzo[a]pyrene is ongoing.
9. Beryllium
a. Background. EPA published the current NPDWR for beryllium on
July 17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an
MCLG and an MCL of 0.004 mg/L. EPA classified beryllium in Group B2,
probable human carcinogen, based on clear evidence of its
carcinogenicity via inhalation or injection in several animal species.
However, EPA also placed beryllium in drinking water Category II for
regulation, based on the weight of evidence for carcinogenicity via
ingestion, and the potency, exposure and pharmacokinetics of this
chemical. EPA derived the MCLG by applying an additional risk
management factor of 10
[[Page 19054]]
to the RfD of 0.005 mg/kg/day (57 FR 31776 at 31785, July 17, 1992
(USEPA, 1992)).
b. Technical Reviews. The Agency updated the health risk assessment
of beryllium in 1998. The 1998 reassessment established a new RfD of
0.002 mg/kg/day and also considered relevant studies on the toxicity of
beryllium including its developmental and reproductive toxicity. The
1998 assessment classified inhaled beryllium as a B1, probable human
carcinogen, using the 1986 cancer guidelines (51 FR 33992, September
24, 1986 (USEPA, 1986b)). Using the 1996 Proposed Guidelines for
Carcinogen Risk Assessment, the 1998 assessment characterized inhaled
beryllium as a ``likely'' carcinogen in humans and concluded that the
human carcinogenic potential of ingested beryllium could not be
determined (61 FR 17960, April 23, 1996 (USEPA, 1996; USEPA, 1998d)).
On this basis, EPA will re-examine the application of the additional
risk management factor of 10 to account for potential carcinogenicity
of beryllium via ingestion that was used when deriving the current
MCLG, if the Agency determines that an MCLG revision is appropriate.
EPA believes that any likely revision to the MCLG for beryllium
could range from 0.01 mg/L to 0.001 mg/L, based on the change in the
RfD in the 1998 assessment, the inclusion or non-inclusion of the risk
management factor, and using a 20 percent relative source contribution
(RSC).\8\ Whereas the 0.01 mg/L value assumes no adjustment for
potential carcinogenicity via oral ingestion (i.e., no 10-fold risk
management factor), the 0.001 mg/L value retains the current risk
management factor of 10.
---------------------------------------------------------------------------
\8\ This is the RSC used for the current MCLG and also the
default value. EPA has no reason to believe that the RSC for
beryllium would change. See Appendix A for a further discussion of
the RSC.
---------------------------------------------------------------------------
Because of changes in the health risk assessment for beryllium, EPA
considered whether analytical feasibility is likely to be a limitation
if the Agency were to lower the MCLG/MCL. The results of the analytical
feasibility analyses indicate that the current PQL of 0.001 mg/L for
beryllium is still appropriate and is unlikely to change. Therefore,
the Agency believes the PQL is unlikely to be a limiting factor if EPA
decides to lower the MCLG/MCL (USEPA, 2002d).
EPA also considered whether treatment feasibility is likely to pose
any limitations if EPA were to lower the MCLG/MCL. The current BATs for
beryllium include activated alumina (AA), ion exchange, lime softening,
coagulation/filtration, and reverse osmosis (RO) with removal
efficiencies ranging from 80 to 99 percent. Small system compliance
technologies also include point-of-use (POU) RO and POU ion exchange.
The Agency believes these BATs are still practical and would not pose
any limitations if the Agency were to lower the MCLG/MCL (USEPA,
2002k).
The results of EPA's review of possible ``other regulatory
revisions'' did not identify any issues which are specific to beryllium
(USEPA, 2002e).
EPA evaluated the results of the occurrence and exposure analyses
for beryllium to determine whether possible changes to the MCLG/MCL
would be likely to result in additional public health protection or an
opportunity for significant cost savings to PWSs and their customers
(USEPA, 2002g; USEPA, 2002h). Table V-3 shows the results of the
detailed occurrence and exposure analysis based on the 16-State cross-
section at the current MCL (0.004 mg/L), the possible lower level of
any MCLG/MCL value (0.001 mg/L), and the possible upper level of any
MCLG/MCL value (0.01 mg/L).
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The results of the detailed occurrence and exposure analysis
indicate that approximately 0.07 percent of the 18,933 systems sampled
in the 16 cross-section States, and approximately 0.02 percent of the
population served by those systems, might be affected if EPA were to
raise the MCLG/MCL. The current BATs and small system compliance
technology for beryllium also apply to other contaminants. In addition
to the removal of beryllium, these treatment technologies have other
beneficial effects (e.g., reduction of hardness or other common
impurities) (USEPA, 2002k). Therefore, if EPA were to raise the MCLG/
MCL, the Agency does not know how many of these PWSs currently treating
to comply with the current MCL of 0.004 mg/L would discontinue any
treatment that is already in place. If, on the other hand, EPA were to
retain the risk management factor and lower the MCLG/MCL, less than 1
percent of the 18,933 systems sampled in the 16 cross-section States
and less than 0.7 percent of the population served by those systems
might be affected.
c. Preliminary Decision. Although there are new data indicating
that it might be possible to revise the MCLG/MCL for beryllium, EPA
does not
[[Page 19056]]
believe a revision to the NPDWR for beryllium, either higher or lower,
is appropriate at this time. The Agency believes that any change in the
MCLG/MCL would be unlikely to significantly improve the level of public
health protection (if EPA were to lower the MCLG/MCL) or provide an
opportunity for significant cost savings to PWSs (if EPA were to raise
the MCLG/MCL).
10. Cadmium
a. Background. EPA published the current NPDWR for cadmium on
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an
MCLG and an MCL of 0.005 mg/L. Because of inadequate dose-response data
to characterize the presence or lack of a carcinogenic hazard from oral
exposure, the Agency regulated cadmium as a Group D carcinogen, not
classifiable as to human carcinogenicity by the oral route of exposure.
Therefore, EPA developed the MCLG for cadmium based on the RfD of
0.0005 mg/kg/day.
b. Technical Reviews. EPA has initiated a reassessment of the
health risks resulting from exposure to cadmium. The revised risk
assessment will consider relevant studies that have become available on
the toxicity of cadmium including its potential developmental and
reproductive toxicity. The Agency expects the new risk assessment to be
completed in the 2002 or 2003 time frame (USEPA, 2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for cadmium is appropriate at this time because a
reassessment of the health risks resulting from exposure to cadmium is
ongoing.
11. Carbofuran
a. Background. EPA published the current NPDWR for carbofuran on
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an
MCLG and an MCL of 0.04 mg/L. EPA based the MCLG on an RfD of 0.005 mg/
kg/day and a cancer classification of E, evidence of non-
carcinogenicity for humans.
b. Technical Reviews. EPA has initiated a reassessment of the
health risks resulting from exposure to carbofuran. The revised risk
assessment will consider relevant studies on the toxicity of carbofuran
including recent data on neurotoxicity and potential developmental and
reproductive toxicity. The Agency expects the new risk assessment to be
completed in the 2002 or 2003 time frame (USEPA, 2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for carbofuran is appropriate at this time because a
reassessment of the health risks resulting from exposure to carbofuran
is ongoing.
12. Carbon Tetrachloride
a. Background. EPA published the current MCLG for carbon
tetrachloride on July 8, 1987 (52 FR 25690 (USEPA, 1987)). The NPDWR
established an MCLG of zero based on a cancer classification of B2,
probable human carcinogen. The NPDWR also established an MCL of 0.005
mg/L based on analytical feasibility.
b. Technical Reviews. EPA has initiated a reassessment of the
health risks resulting from exposure to carbon tetrachloride. The
revised risk assessment will consider relevant studies that have become
available on the toxicity of carbon tetrachloride including its
potential developmental and reproductive toxicity. The Agency expects
the new risk assessment to be completed in the 2002 or 2003 time frame
(USEPA, 2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for carbon tetrachloride is appropriate at this time because
a reassessment of the health risks resulting from exposure to carbon
tetrachloride is ongoing.
13. Chlordane
a. Background. EPA published the current NPDWR for chlordane on
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an
MCLG of zero based on a cancer classification of B2, probable human
carcinogen. The NPDWR also established an MCL of 0.002 mg/L based on
analytical feasibility.
b. Technical Reviews. EPA updated its risk assessment for chlordane
in 1998 (USEPA, 1998e). That assessment included an evaluation of
developmental and reproductive endpoints. The assessment also retained
the B2 cancer classification, concluding that chlordane is a probable
human carcinogen using the 1986 EPA Guidelines for Carcinogen Risk
Assessment (51 FR 33992, September 24, 1986 (USEPA, 1986b)). Under the
1996 Proposed Guidelines for Carcinogen Risk Assessment (61 FR 17960,
April 23, 1996 (USEPA, 1996)), chlordane is characterized as a likely
carcinogen by all routes of exposure and, at the present time, would
require quantification using a linear dose response, thus, the MCLG of
zero remains appropriate.
EPA based the current MCL for chlordane on a PQL of 0.002 mg/L. As
a part of the Six-Year Review, EPA analyzed more recent WS data to
determine if it might be possible to recalculate the PQL (USEPA,
2002d). In addition, the Agency evaluated whether more sensitive
analytical methods have been approved and put into use by a wide number
of laboratories. The results of these analyses indicate that only a
slight improvement in analytical feasibility might exist. Evaluation of
the WS data shows that EPA Regional and State laboratories exhibit
greater than 85 percent laboratory passing rates at concentrations
around the current PQL of 0.002 mg/L. Because most of the laboratory
passing rates exceeded the 75 percent criterion typically used to
derive a PQL from WS studies, this information indicates that a lower
PQL corresponding to the 75 percent passing rate might exist for
chlordane. While this information is indicative of a possibly lower
PQL, the WS data are insufficient at this time to actually recalculate
what the lower PQL for chlordane might be.
Using information about the analytical methods most widely used to
report results in the WS studies, the MDLs for these methods, and the
10 times MDL multiplier, EPA estimated what the possibly lower PQL/MCL
might be. For the analysis of chlordane in the more recent WS studies,
laboratories predominantly used EPA Methods 505 (Gas Chromatography
with microextraction) and 508 (Gas Chromatography with Electron Capture
Detector), which have MDLs of 0.00014 mg/L and 0.0000041 mg/L,
respectively. A 10 times MDL multiplier predicts that the PQL could
range from 0.0014 mg/L to 0.000041 mg/L. EPA averaged these two values,
rounded up to 0.001 mg/L, and used this value as a threshold in the
occurrence analysis discussed in this section.
Since the analytical feasibility analysis indicates that the PQL
for chlordane (and therefore the MCL) could possibly be lower if EPA
had more definitive data to recalculate the PQL, EPA considered whether
treatment feasibility is likely to pose any limitations (USEPA, 2002k).
The current BAT for chlordane is GAC. Small system compliance
technologies for chlordane include GAC, POU GAC, and powdered activated
carbon (PAC). Because chlordane is a moderately adsorbed pesticide, EPA
believes that GAC is still a practical treatment and would not pose any
limitations for chlordane at a possibly lower MCL.
The results of EPA's review of possible ``other regulatory
revisions'' did not identify any issues which are specific to chlordane
(USEPA, 2002e).
[[Page 19057]]
EPA evaluated the results of the occurrence and exposure analyses
for chlordane to determine whether changes to the MCL might be
appropriate and likely to result in additional public health protection
if the PQL were recalculated (USEPA, 2002g; USEPA, 2002h). Table V-4
shows the results of the detailed occurrence and exposure analysis
based on the 16-State cross-section for the current MCL (0.002 mg/L)
and the possible PQL/MCL based on the analytical feasibility analysis
(0.001 mg/L).
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The detailed occurrence and exposure analysis indicates that
chlordane is unlikely to occur at the current MCL or any potential MCL
revision for the States used in the cross-section. Since chlordane uses
were canceled in the United States in 1988 and since it is subject to
the United Nations Prior Informed Consent procedure (USEPA, 2002g;
USEPA, 2002h), EPA expects the occurrence of chlordane in PWSs to be
rare.
c. Preliminary Decision. Although there are new data that support
consideration of a slightly lower PQL (and therefore a possibly lower
MCL), EPA does not believe a revision to the NPDWR for chlordane is
appropriate at this time. The Agency does not have sufficient data at
this time on which to base a PQL recalculation and hence an MCL
revision. Also, the Agency believes that any change in the PQL would be
minimal and unlikely to significantly improve the level of public
health protection because chlordane appears to occur infrequently at
concentrations at or below the current MCL.
14. Chromium
a. Background. EPA published the current NPDWR for total chromium
on January 31, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established
an MCLG and MCL of 0.1 mg/L. Although the NPDWR regulates total
chromium, the adverse health effects associated with hexavalent
chromium (chromium VI) are the basis of the current MCLG since that is
the more toxic species (56 FR 3526, January 31, 1991 (USEPA, 1991a)).
EPA based the MCLG on an RfD of 0.005 mg/kg/day and an assumed RSC from
water of 70 percent for total chromium (refer to Appendix A for a
description of the RSC). EPA regulated chromium as a Group D
carcinogen, not classifiable as to human carcinogenicity by the oral
route of exposure.
b. Technical Reviews. The Agency updated the risk assessment for
chromium in 1998 (USEPA, 1998f). The revised risk assessment considered
relevant studies that were available on the toxicity of chromium
including potential developmental and reproductive toxicity. Based on
the revised risk assessment, EPA has identified changes in the health
risk assessment that support consideration of whether it may be
appropriate to revise the MCLG and MCL (USEPA, 2002i). The 1998
assessment revised the RfD for hexavalent chromium (chromium VI) from
0.005 mg/kg/day to
[[Page 19058]]
0.003 mg/kg/day based on a modification to the original uncertainty
factor and the addition of a modifying factor because of data on the
potential for gastrointestinal effects in humans as a result of oral
exposures. The critical study used as the basis for the RfD did not
change.
The 1998 assessment of chromium VI made no change to the cancer
classification of Group D for oral exposures and determined that the
carcinogenicity of chromium VI cannot be determined because of a lack
of sufficient epidemiological or toxicological studies under the 1996
Proposed Guidelines for Carcinogen Risk Assessment. Chromium VI is a
Group A known human carcinogen by the inhalation route of exposure.
Public concern over the adverse health effects of chromium VI has
increased in recent years. One issue is whether chromium VI is a human
carcinogen through oral ingestion. In 2001, the State of California
convened a Blue Ribbon Panel to evaluate the available data on this
issue. The Panel issued its report in August 2001 (Flegal et al., 2001)
and found no basis in either the epidemiological or animal data
published in the literature for concluding that orally ingested
chromium VI is a carcinogen. The National Toxicology Program (NTP) has
agreed to study the chronic toxicity and carcinogenicity of chromium VI
after oral exposure. That effort will include shorter-term toxicity
studies, two-year rodent toxicity and carcinogenicity studies as well
as bioavailability, distribution, and mechanistic studies. NTP expects
the results to be available in the next three to five years (NTP,
2001).
The availability of new data on the contribution of dietary
chromium to total chromium exposure supports a re-evaluation of the RSC
(NAS, 2001). The Agency applied an RSC of 70 percent in determining the
current MCLG. Using the new Agency RfD of 0.003 mg/kg/day along with
the application of 20 percent, 50 percent, or 70 percent as RSC values,
the Agency believes that any likely revisions to the MCLG could range
from 0.02 mg/L to 0.07 mg/L. A general evaluation of the data indicates
that a revised RSC would likely fall within the 20 percent to 50
percent range.
Because the results of the health effects review support
consideration of whether it may be appropriate to revise the NPDWR for
chromium based on changes in the RfD and possible changes in the RSC
assumptions, EPA considered whether analytical feasibility is likely to
be a limitation. The results of the analytical feasibility analyses
indicate that the current PQL of 0.01 mg/L for chromium is still
appropriate and is unlikely to change. Therefore, the Agency believes
the PQL is unlikely to be a limiting factor if EPA decides to revise
the MCLG/MCL (USEPA, 2002d).
EPA also considered whether treatment feasibility is likely to pose
any limitations if EPA were to revise the MCLG/MCL. The current BATs
for chromium include ion exchange, lime softening, coagulation/
filtration, and RO. Small system compliance technologies also include
POU RO and POU ion exchange. At the present time, EPA believes these
BATs are still practical and would not pose any limitations if the
Agency were to revise the MCLG/MCL (USEPA, 2002k).
The results of EPA's review of possible ``other regulatory
revisions'' did not identify any issues which are specific to chromium
(USEPA, 2002e).
EPA evaluated the results of the occurrence and exposure analyses
for chromium to determine whether a revised MCLG/MCL would be likely to
result in additional public health protection (USEPA, 2002g; USEPA,
2002h). Table V-5 shows the results of the detailed occurrence and
exposure analysis based on the 16-State cross-section for the current
MCLG/MCL (0.1 mg/L), the possible MCLG/MCL value retaining the 70
percent RSC (0.07 mg/L), the possible MCLG/MCL value using a 50 percent
RSC (0.05 mg/L), and the possible MCLG/MCL value using a 20 percent RSC
(0.02 mg/L).
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The results of detailed occurrence and exposure analysis indicate
that less than 0.4 percent of the 19,695 systems sampled in the 16
cross-section States and approximately 0.1 percent of the population
served by those systems, might be affected if EPA were to lower the MCL
to 0.02 mg/L.
c. Preliminary Decision. Although EPA has identified a change to
the RfD on which the current MCLG for chromium is based, the Agency
believes that a decision to revise the chromium NPDWR at this time is
premature in light of the ongoing NTP studies on the toxicology and
carcinogenicity of hexavalent chromium. The Agency is aware of
considerable public controversy on the subject of the appropriate level
for chromium in drinking water and realizes there are differing views
regarding the severity of the health effects of chromium in water, the
relative importance of drinking water as a source of chromium as
compared with other sources, and the chemical form that should serve as
the basis for regulating chromium (total versus hexavalent chromium).
Because the NTP studies will not be available in time for the final
revise/not revise decision, EPA is placing chromium in the ``not
revise--data gap'' category. When completed, the NTP results will be
considered either in the next review round or sooner, if the Agency
deems it appropriate.
15. Copper
a. Background. EPA published the current NPDWR for copper on June
7, 1991 (56 FR 26460 (USEPA, 1991b)). The NPDWR established an MCLG of
1.3 mg/L, based on a lowest-observed-adverse-effect level (LOAEL) of
5.3 mg/day \9\, and an action level of 1.3 mg/L for first-draw samples
at the 90th percentile of taps tested. The NPDWR requires water systems
to monitor for copper at the tap. Water systems must optimize corrosion
control. This requires water systems serving more than 50,000 persons
and those smaller size systems that exceed the copper action level to
install corrosion control treatment and to monitor for specified water
quality control parameters. The regulation also requires any size
system that exceeds the copper action level to monitor for copper in
source water and, if appropriate, to install source water treatment.
EPA published revisions to the copper NPDWR on January 12, 2000 (65 FR
1950 (USEPA, 2000a)). These revisions made changes to monitoring and
reporting requirements but did not affect the copper MCLG, action
level, or basic TT requirements.
---------------------------------------------------------------------------
\9\ In June 1994, EPA published a technical amendment that
provided additional information on the basis of the copper MCLG (59
FR 33860, June 30, 1994 (USEPA, 1994b)).
---------------------------------------------------------------------------
b. Technical Reviews. In 1999, EPA requested that the National
Research Council (NRC) of the NAS examine the available nutritional and
toxicological data for copper and provide a recommendation regarding
the levels in drinking water that are associated with adverse effects.
The NRC concluded that copper in drinking water could produce adverse
gastrointestinal effects in some individuals at concentrations of about
3 mg/L or greater. In addition, the NRC advised that individuals who
carry a recessive gene for Wilson's disease could accumulate excess
copper in their livers at these same concentrations. Accordingly, the
NAS recommended that EPA retain the MCLG of 1.3 mg/L while additional
data are collected on the risk to the carriers of the Wilson's Disease
gene and other populations that may accumulate copper in their livers
(NAS, 2000a).
EPA has initiated an assessment of health risks resulting from
exposure to copper that will include the findings of NAS as well as
more recently published data (USEPA, 2002i). This assessment will
consider relevant studies on the toxicity of copper including its
effects on genetically and developmentally sensitive populations. The
Agency expects the new risk assessment to be completed in the 2002 or
2003 time frame (USEPA, 2002i).
EPA has received comments on the copper NPDWR suggesting that EPA
discontinue copper as a regulated contaminant or change it to a
secondary standard (USEPA, 2002e). EPA is not aware of any new
information that would warrant such a revision.
EPA has identified several potential research needs which may be
considered in the context of an overall drinking water research
strategy. These research needs are described in the ``Water Treatment
Technology Feasibility Support Document for Chemical Contaminants; In
Support of EPA Six-Year Review of National Primary Drinking Water
Regulations'' (USEPA, 2002k).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for copper is appropriate at this time because a reassessment
of the health risks resulting from exposure to copper is ongoing.
Several potential research needs were identified for copper. The NAS
review of copper in drinking water concluded that there was a need to
conduct research that would characterize copper-sensitive populations
(both population size and the factors leading to sensitivity) and
further define the contribution of copper from drinking water to total
copper intake (NAS, 2000a). Treatment-related research needs for copper
are described in the Six-Year Review treatment feasibility support
document (USEPA, 2002k).
16. Cyanide
a. Background. EPA published the current NPDWR for cyanide on July
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG and
MCL of 0.2 mg/L. The MCLG was developed based on an RfD of 0.02 mg/kg/
day and a cancer classification of D, not classifiable as to human
carcinogenicity.
b. Technical Reviews. The results of the health effects technical
review identified some information on reproductive effects from the
ATSDR toxicological profile that indicate the need to update the
Agency's risk assessment for cyanide (USEPA, 2002i). In light of this
information, EPA has initiated a reassessment of the health risks
resulting from exposure to cyanide and has already solicited scientific
information from the public for consideration (67 FR 1212, January 9,
2002 (USEPA, 2002a)). The new risk assessment will consider relevant
data on the toxicity of cyanide including its potential developmental
and reproductive toxicity. Because the new assessment is not expected
to be completed until the 2004 or 2005 time frame, EPA does not believe
it is appropriate to revise the MCLG at this time.
A review of analytical or treatment feasibility is not necessary
for cyanide because changes to the MCLG are not warranted at this time
and the current MCL is set at the MCLG. EPA's review of ``other
regulatory revisions'' identified a potential revision relating to an
error in the BAT specified for cyanide in the CFR (USEPA, 2002e). The
CFR currently specifies ``chlorine'' as a BAT for cyanide for
compliance with the MCL and with variance and exemption requirements
(40 CFR 141.62 and 142.62, respectively); however, the CFR should
specify ``alkaline chlorination'', as BAT. EPA plans to correct this
error through a technical amendment to the cyanide NPDWR in the near
future. In the meantime, water systems and States should continue to be
guided by the ``Public Water System Warning: Cyanide'' (USEPA, 1994a)
that EPA distributed through its regional offices. The warning includes
information on the use of chlorination (non-alkaline) and the potential
for formation of harmful cyanogen chloride due to reaction of chlorine
with cyanide
[[Page 19061]]
in water under those conditions. The PWS Warning explains this process
in detail and outlines treatment practice, including contact times,
required chlorine concentrations, and compensation for temperature
effects. The July 25, 1990 proposed regulation for cyanide discusses
the effectiveness of oxidation of cyanide at high pH levels (55 FR
30370 at 30419 (USEPA, 1990)) and the PWS Warning discusses mitigation
of the formation of cyanogen chloride. This information is also
summarized in the six-year review treatment technology support document
(USEPA, 2002k).
Since the potential regulatory revision identified by these
analyses does not affect the MCLG or the MCL, EPA does not believe it
is necessary to conduct a detailed occurrence and exposure analysis for
cyanide.
c. Preliminary Decision. Other than the technical amendment to
correct the BAT, EPA does not believe a revision to the NPDWR for
cyanide is appropriate at this time. A reassessment of the health risks
has been initiated and the Agency does not believe it is appropriate to
revise the NPDWR while that effort is in process.
17. 2,4-D (2,4-Dichlorophenoxyacetic Acid)
a. Background. EPA published the NPDWR for 2,4-D on January 30,
1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an MCLG and an
MCL of 0.07 mg/L. EPA developed the MCLG based on a RfD of 0.01 mg/kg/
day and a cancer classification of D, not classifiable as to human
carcinogenicity.
b. Technical Reviews. EPA has initiated a reassessment of the
health risks resulting from exposure to 2,4-D. The revised risk
assessment will consider relevant studies that have become available on
the toxicity of 2,4-D including its potential developmental and
reproductive toxicity. EPA expects the new risk assessment to be
completed in the 2003 or 2004 time frame (USEPA, 2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for 2,4-D is appropriate at this time because a reassessment
of the health risks resulting from exposure to 2,4-D is ongoing.
18. Dalapon (2,2-Dichloropropionic Acid)
a. Background. EPA published the current NPDWR for dalapon on July
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG and
an MCL of 0.2 mg/L. EPA developed the MCLG based on an RfD of 0.03 mg/
kg/day and a cancer classification of D, not classifiable as to human
carcinogenicity.
b. Technical Reviews. The Agency has not updated the health risk
assessment for dalapon since the NPDWR was published. Therefore, as
part of the Six-Year Review process, EPA conducted a literature search
for relevant data on the toxicology of dalapon, including its potential
developmental and reproductive toxicity. The literature search did not
identify any studies that warrant a review of the RfD or the cancer
classification (USEPA, 2002i).
A review of analytical or treatment feasibility is not necessary
for dalapon because changes to the MCLG are not warranted at this time
and the current MCL is set at the MCLG. In addition, the results of
EPA's review of possible ``other regulatory revisions'' did not
identify any dalapon-specific issues (USEPA, 2002e). Since EPA did not
identify a health or technology basis for revising the dalapon NPDWR,
the Agency did not conduct a detailed occurrence and exposure analysis.
c. Preliminary Decision. After reviewing the results of the
pertinent technical analyses, the Agency believes the NPDWR for dalapon
remains appropriate and thus, it is not subject to revision at this
time.
19. 1,2-Dibromo-3-chloropropane (DBCP)
a. Background. EPA published the current NPDWR for DBCP on January
30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an MCLG of
zero based on a cancer classification of B2, probable human carcinogen.
The NPDWR also established an MCL of 0.0002 mg/L based on analytical
feasibility.
b. Technical Reviews. The Agency has not updated the health risk
assessment for DBCP since the NPDWR was published; however, ATSDR
completed a toxicological profile for DBCP in 1992 (ATSDR, 1992). This
assessment and other recent information do not warrant a review of the
cancer classification because there are inadequate data to support a
nonlinear dose response relationship (USEPA, 2002i). Accordingly, the
MCLG remains at zero and the Agency believes that a further review of
the health effects of DBCP is not warranted at this time.
EPA based the current MCL for DBCP on a PQL of 0.0002 mg/L. As a
part of the Six-Year Review, EPA analyzed more recent WS data to
determine if it might be possible to recalculate the PQL (USEPA,
2002d). In addition, the Agency evaluated whether more sensitive
analytical methods have been approved and put into use by a wide number
of laboratories. The results of these analyses indicate that a slight
improvement in analytical feasibility might exist. Evaluation of the WS
data shows that EPA Regional and State laboratories exhibit greater
than 85 percent laboratory passing rates at concentrations around the
current PQL of 0.0002 mg/L. Because most of the laboratory passing
rates exceeded the 75 percent criterion typically used to derive a PQL
from WS studies, this information indicates that a lower PQL
corresponding to the 75 percent passing rate might exist for DBCP.
While this information is indicative of a possibly lower PQL, the WS
data are insufficient at this time to actually recalculate what the
lower PQL for DBCP might be.
Using information about the analytical methods most widely used to
report results in the WS studies, the MDLs for these methods, and the
10 times MDL multiplier, EPA estimated what the possibly lower PQL/MCL
might be. For the analysis of DBCP in the more recent WS studies,
laboratories predominantly used EPA Method 504.1 (Gas Chromatography
with microextraction), which has an MDL of 0.00001 mg/L. A 10 times MDL
multiplier predicts that the PQL may be around 0.0001 mg/L (also one-
half the current MCL). The 0.0001 mg/L value is used as a threshold in
the occurrence analysis, which is discussed in this section.
Since the analytical feasibility analysis indicates that the PQL
for DBCP (and therefore the MCL) could possibly be lower if EPA had
more definitive data to recalculate the PQL, EPA considered whether
treatment feasibility is likely to pose any limitations (USEPA, 2002k).
The BATs for DBCP include aeration and GAC. Small system compliance
technologies for DBCP include GAC, POU GAC, PAC, and several aeration
technologies. Since the Henry's Law coefficient for DBCP is relatively
low (i.e., DBCP is ``less strippable'' than other contaminants), GAC
may in some cases be the preferred treatment. Considering that only a
slight improvement in analytical feasibility may exist, EPA believes
that these BATs are still practical and would not pose any limitations
for DBCP at a possibly lower MCL.
The results of EPA's review of possible ``other regulatory
revisions'' did not identify any issues which are specific to DBCP
(USEPA, 2002e).
EPA evaluated the results of the detailed occurrence and exposure
analyses for DBCP to determine whether changes to the MCL might be
appropriate and likely to result in additional public health protection
if
[[Page 19062]]
the PQL were recalculated (USEPA, 2002g; USEPA, 2002h). Table V-6 shows
the results of the detailed occurrence and exposure analysis based on
the 16-State cross-section at the current MCL (0.0002 mg/L) and the
possible PQL/MCL based on the analytical feasibility analysis (0.0001
mg/L).
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The results of detailed occurrence and exposure analysis indicate
that approximately 0.5 percent of the 14,042 systems sampled in the 16
cross-section States and approximately 0.6 percent of the population
served by those systems, might be affected if EPA were to gather the
information to recalculate the PQL (estimated to be around 0.0001 mg/L)
and to revise the MCL accordingly.
c. Preliminary Decision. Although there are new data that support
consideration of a slightly lower PQL (and therefore a possibly lower
MCL), EPA does not believe a revision to the NPDWR for DBCP is
appropriate at this time. The Agency does not have sufficient data at
this time on which to base a PQL recalculation and hence an MCL
revision. In addition, because the occurrence of DBCP appears to be
minimal between the current MCL and any likely PQL/MCL revision, the
Agency believes that any potential revisions to the DBCP NPDWR are
unlikely to significantly improve the level of public health
protection.
20. 1,2-Dichlorobenzene (o-Dichlorobenzene)
a. Background. EPA published the current NPDWR for 1,2-
dichlorobenzene on January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The
NPDWR established an MCLG and an MCL of 0.6 mg/L. EPA developed the
MCLG based on an RfD of 0.09 mg/kg/day and a cancer classification of
D, not classifiable as to human carcinogenicity.
b. Technical Reviews. EPA has initiated a reassessment of the
health risks resulting from exposure to 1,2-dichlorobenzene. The
revised risk assessment will consider relevant studies on the toxicity
of 1,2-dichlorobenzene including its potential developmental and
reproductive toxicity. The Agency expects the new risk assessment to be
completed in the 2002 or 2003 time frame (USEPA, 2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for 1,2-dichlorobenzene is appropriate at this time because a
reassessment of the health risks resulting from exposure to 1,2-
dichlorobenzene is ongoing.
[[Page 19063]]
21. 1,4-Dichlorobenzene (p-Dichlorobenzene)
a. Background. EPA published the current NPDWR for 1,4-
dichlorobenzene on July 8, 1987 (52 FR 25690 (USEPA, 1987)). The NPDWR
established an MCLG and an MCL of 0.075 mg/L. EPA developed the MCLG
based on an RfD of 0.1 mg/kg/day and a cancer classification of C,
possible human carcinogen.
b. Technical Reviews. EPA has initiated a reassessment of the
health risks resulting from exposure to 1,4-dichlorobenzene. The
revised risk assessment will consider relevant studies on the toxicity
of 1,4-dichlorobenzene including its potential developmental and
reproductive toxicity. The Agency expects the new risk assessment to be
completed in the 2002 or 2003 time frame (USEPA, 2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for 1,4-dichlorobenzene is appropriate at this time because a
reassessment of the health risks resulting from exposure to 1,4-
dichlorobenzene is ongoing.
22. 1,2-Dichloroethane (Ethylene Dichloride)
a. Background. EPA published the current NPDWR for 1,2-
dichloroethane on July 8, 1987 (52 FR 25690 (USEPA, 1987)). The NPDWR
established an MCLG of zero based on a cancer classification of B2,
probable human carcinogen. The NPDWR also established an MCL of 0.005
mg/L based on analytical feasibility.
b. Technical Reviews. EPA has initiated a reassessment of the
health risks resulting from exposure to 1,2-dichloroethane. The revised
risk assessment will consider relevant studies that have become
available on the toxicity of 1,2-dichloroethane including potential
developmental and reproductive toxicity. The Agency expects the new
risk assessment to be completed in the 2002 or 2003 time frame (USEPA,
2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for 1,2-dichloroethane is appropriate at this time because a
reassessment of the health risks resulting from exposure to 1,2-
dichloroethane is ongoing.
23. 1,1-Dichloroethylene
a. Background. EPA published the current NPDWR for 1,1-
dichloroethylene on July 8, 1987 (52 FR 25690 (USEPA, 1987)). The NPDWR
established an MCLG and an MCL of 0.007 mg/L. The Agency developed the
MCLG based on an RfD of 0.009 mg/kg/day and a cancer classification of
C, possible human carcinogen.
b. Technical Reviews. EPA has initiated a reassessment of the
health risks resulting from exposure to 1,1-dichloroethylene. The
revised risk assessment will consider relevant studies on the toxicity
of 1,1-dichloroethylene including its potential developmental and
reproductive toxicity. The Agency expects the new risk assessment to be
completed in the 2002 or 2003 time frame (USEPA, 2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for 1,1-dichloroethylene is appropriate at this time because
a reassessment of the health risks resulting from exposure to 1,1-
dichloroethylene is ongoing.
24. cis-1,2-Dichloroethylene
a. Background. EPA published the current NPDWR for cis-1,2-
dichloroethylene on January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The
NPDWR established an MCLG and MCL of 0.07 mg/L. The Agency developed
the MCLG based on an RfD of 0.01 mg/kg/day and a cancer classification
of D, not classifiable as to human carcinogenicity.
b. Technical Reviews. The Agency has not updated the health risk
assessment for cis-1,2-dichloroethylene since the NPDWR was published;
however, ATSDR completed a toxicological profile for cis-1,2-
dichloroethylene in 1996 (ATSDR, 1996a). This review did not find data
that would warrant a review of the RfD or cancer classification. As
part of the Six-Year Review process, EPA conducted a literature search
for relevant data on the toxicology of cis-1,2-dichloroethylene,
including its potential developmental and reproductive toxicity. The
literature search did not identify any studies that warrant a review of
the RfD or the cancer classification (USEPA, 2002i).
A review of analytical or treatment feasibility is not necessary
for cis-1,2-dichloroethylene because changes to the MCLG are not
warranted at this time and the current MCL is set at the MCLG. In
addition, the results of EPA's review of possible ``other regulatory
revisions'' did not identify any issues that were specific to cis-1,2-
dichloroethylene (USEPA, 2002e). Since EPA did not identify a health or
technology basis for revising the cis-1,2-dichloroethylene NPDWR, the
Agency did not conduct a detailed occurrence and exposure analysis.
c. Preliminary Decision. After reviewing the results of the
pertinent technical analyses, the Agency believes the NPDWR for cis-
1,2-dichloroethylene remains appropriate and thus, it is not subject to
revision at this time.
25. trans-1,2-Dichloroethylene
a. Background. EPA published the current NPDWR for trans-1,2-
dichloroethylene on January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The
NPDWR established an MCLG and an MCL of 0.1 mg/L. The Agency developed
the MCLG based on an RfD of 0.02 mg/kg/day and a cancer classification
of D, not classifiable as to human carcinogenicity.
b. Technical Reviews. The Agency has not updated the health risk
assessment for trans-1,2-dichloroethylene since the NPDWR was
published; however, ATSDR completed a toxicological profile for trans-
1,2-dichloroethylene in 1996 (ATSDR, 1996a). This review did not find
data that would warrant a review of the RfD or cancer classification.
As part of the Six-Year Review process, EPA conducted a literature
search for relevant data on the toxicology of trans-1,2-
dichloroethylene, including its potential developmental and
reproductive toxicity. The literature search did not identify any
studies that warrant a review of the RfD or the cancer classification
(USEPA, 2002i).
A review of analytical or treatment feasibility is not necessary
for trans-1,2-dichloroethylene because changes to the MCLG are not
warranted at this time and the current MCL is set at the MCLG. In
addition, the results of EPA's review of possible ``other regulatory
revisions'' did not identify any issues that were specific to trans-
1,2-dichloroethylene (USEPA, 2002e). Since EPA did not identify a
health or technology basis for revising the trans-1,2-dichloroethylene
NPDWR, the Agency did not conduct a detailed occurrence and exposure
analysis.
c. Preliminary Decision. After reviewing the results of the
pertinent technical analyses, the Agency believes the NPDWR for trans-
1,2-dichloroethylene remains appropriate and thus, it is not subject to
revision at this time.
26. Dichloromethane (Methylene Chloride)
a. Background. EPA published the NPDWR for dichloromethane on July
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG of
zero based on a cancer classification of B2, probable human carcinogen.
The NPDWR also established an MCL of 0.005 mg/L based on analytical
feasibility.
[[Page 19064]]
b. Technical Reviews. The Agency has not updated the health risk
assessment for dichloromethane since the NPDWR was published; however,
ATSDR completed a toxicological profile for dichloromethane in 2000
(USEPA, 2002i). This review did not find any data that would warrant a
change in the cancer classification on which the 1992 zero MCLG is
based. The ATSDR toxicological profile considered relevant studies on
the toxicity of dichloromethane including developmental and
reproductive toxicity.
The current MCL for dichloromethane is based on a PQL of 0.005 mg/
L. As a part of the Six-Year Review, EPA analyzed more recent WS data
to determine if it might be possible to recalculate the PQL (USEPA,
2002d). In addition, the Agency evaluated whether more sensitive
analytical methods have been approved and put into use by a wide number
of laboratories. The analysis of the WS data indicates that a slight
improvement in analytical feasibility might exist. Evaluation of the WS
data shows that EPA Regional and State laboratories exhibit greater
than 90 percent laboratory passing rates at concentrations around the
current PQL of 0.005 mg/L. Because most of the laboratory passing rates
exceeded the 75 percent criterion typically used to derive a PQL from
WS studies, this information indicates that a lower PQL corresponding
to the 75 percent passing rate might exist for dichloromethane. While
this information is indicative of a possibly lower PQL, the WS data are
insufficient at this time to actually recalculate what the lower PQL
for dichloromethane might be.
Using information about the analytical methods most widely used to
report results in the WS studies, the MDLs for these methods, and the
10 times MDL multiplier, EPA estimated what the possibly lower PQL/MCL
might be. For the analysis of dichloromethane in the more recent WS
studies, laboratories predominantly used EPA Methods 524.2 (GC/MS) and
502.2 (Purge and Trap Gas Chromatography), which have MDLs of 0.00003
mg/L and 0.00002 mg/L, respectively. A 10 times MDL multiplier predicts
that the PQL may be around 0.0003 to 0.0002 mg/L. The Agency used the
average of these two values (0.00025 mg/L) as a threshold (i.e.,
possible PQL) in the occurrence analysis discussed in this section.
Since the analytical feasibility analysis indicates that the PQL
for dichloromethane (and therefore the MCL) could possibly be lower if
EPA had more definitive data to recalculate the PQL, EPA considered
whether treatment feasibility is likely to pose any limitations (USEPA,
2002k). The current BAT for dichloromethane is PTA. EPA believes this
BAT is still practical and would not pose any limitations for
dichloromethane at a possibly lower MCL.
The results of EPA's review of possible ``other regulatory
revisions'' did not identify any dichloromethane-specific issues
(USEPA, 2002e).
EPA evaluated the results of the occurrence and exposure analyses
for dichloromethane to determine whether changes to the MCL might be
appropriate and likely to result in additional public health protection
if the PQL were recalculated (USEPA, 2002g; USEPA, 2002h). Table V-7
shows the results of the detailed occurrence and exposure analysis
based on the 16-State cross-section for the current MCL (0.005 mg/L)
and the possible PQL/MCL based on the analytical feasibility analysis
(0.00025 mg/L).
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The results of the detailed occurrence and exposure analysis
indicate that less than 5 percent of the 21,530 systems sampled in the
16 cross-section States and slightly more than 9 percent of the
population served by those systems, might be affected if EPA were to
gather information to recalculate the PQL (to a lower PQL of around
0.00025 mg/L) and revise the MCL accordingly.
c. Preliminary Decision. EPA does not believe it is appropriate to
revise the NPDWR for dichloromethane at this time because the data
indicating the possibility of a PQL/MCL revision are not sufficient to
support a regulatory revision at this time. However, EPA believes there
may be an opportunity for improvement in the level of public health
protection if the Agency had sufficient data to recalculate the PQL.
The Agency therefore solicits comment on whether to gather better data
on which to recalculate the PQL. Any such effort is unlikely to be
completed in time to inform the revise/not revise decision for the
final notice but may provide new information for consideration during
the next six-year review cycle.
27. 1,2-Dichloropropane
a. Background. EPA published the current NPDWR for 1,2-
dichloropropane on January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The
NPDWR established an MCLG of zero based on a cancer classification of
B2, probable human carcinogen. The NPDWR also established an MCL of
0.005 mg/L based on analytical feasibility.
b. Technical Reviews. EPA has not identified any new information
that indicates that it is appropriate to revise the cancer
classification for 1,2-dichloropropane at this time (USEPA, 2002i).
Because the MCLG remains at zero, the Agency believes that a further
review of the health effects of 1,2-dichloropropane is not warranted at
this time.
The current MCL for 1,2-dichloropropane is based on a PQL of 0.005
mg/L. As a part of the Six-Year Review, EPA analyzed more recent WS
data to determine if it might be possible to recalculate the PQL
(USEPA, 2002d). In addition, the Agency evaluated whether more
sensitive analytical methods have been approved and put into use by a
wide number of laboratories. The results of these analyses indicate
that some improvement in analytical feasibility might exist. Evaluation
of the WS data shows that EPA Regional and State laboratories exhibit
greater than 95 percent laboratory passing rates at concentrations
around the current PQL of 0.005 mg/L. Because most of the laboratory
passing rates exceeded the 75 percent criterion typically used to
derive a PQL from WS studies, this information indicates that a lower
PQL corresponding to the 75 percent passing rate might exist for 1,2-
dichloropropane. While this information is indicative of
[[Page 19066]]
a possibly lower PQL, the WS data are insufficient at this time to
actually recalculate what the lower PQL for 1,2-dichloropropane might
be.
Using information about the analytical methods most widely used to
report results in the WS studies, the MDLs for these methods, and the
10 times MDL multiplier, EPA estimated what the possibly lower PQL/MCL
might be. For the analysis of 1,2-dichloropropane in the more recent WS
studies, laboratories predominantly used EPA Methods 524.2 (GC/MS) and
502.2 (Purge and Trap Gas Chromatography), which have MDLs of 0.00004
mg/L and 0.00003 mg/L, respectively. A 10 times MDL multiplier predicts
that the PQL may be around 0.0004 to 0.0003 mg/L. EPA used the 0.0004
mg/L value as a threshold in the occurrence analysis discussed in this
section.
Since the analytical feasibility analysis indicates that the PQL
for 1,2-dichloropropane (and therefore the MCL) could possibly be lower
if EPA had more definitive data to recalculate the PQL, EPA considered
whether treatment feasibility is likely to pose any limitations (USEPA,
2002k). The current BATs for 1,2-dichloropropane are GAC and PTA. Small
system compliance technologies for 1,2-dichloropropane include GAC,
PTA, and several other aeration technologies. EPA believes that these
BATs are still practical and would not pose any limitations for 1,2-
dichloropropane at a possibly lower MCL.
The results of EPA's review of possible ``other regulatory
revisions'' did not identify any issues that are specific to 1,2-
dichloropropane (USEPA, 2002e).
EPA evaluated the results of the occurrence and exposure analyses
for 1,2-dichloropropane to determine whether changes to the MCL might
be appropriate and likely to result in additional public health
protection if the PQL were recalculated (USEPA, 2002g; USEPA, 2002h).
Table V-8 shows the results of the detailed occurrence and exposure
analysis based on the 16-State cross-section for the current MCL (0.005
mg/L) and the possible PQL/MCL based on the analytical feasibility
analysis (0.0004 mg/L).
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The results of the detailed occurrence and exposure analysis
indicate that less than 0.05 percent of the 21,988 systems sampled in
the 16 cross-section States and approximately 0.1 percent of the
population served by those systems, might be affected if EPA were to
gather the information to recalculate the PQL
[[Page 19067]]
(to a lower PQL of around 0.0004 mg/L) and revise the MCL accordingly.
c. Preliminary Decision. Although there are new data that support
consideration of a possibly lower PQL (and therefore a possibly lower
MCL), EPA does not believe a revision to the NPDWR for 1,2-
dichloropropane is appropriate at this time. The Agency does not have
sufficient data at this time on which to base a PQL recalculation and
hence an MCL revision. In addition, because the occurrence of 1,2-
dichloropropane appears to be minimal between the current MCL and any
likely PQL/MCL revision, the Agency believes that any potential
revisions to the 1,2-dichloropropane NPDWR are unlikely to
significantly improve the level of public health protection.
28. Di(2-ethylhexyl)adipate (DEHA)
a. Background. EPA published the NPDWR for DEHA on July 17, 1992
(57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG and an MCL
of 0.4 mg/L. The Agency developed the MCLG based on an RfD of 0.6 mg/
kg/day and a cancer classification of C, possible human carcinogen.
b. Technical Reviews. The Agency has identified data that indicate
it may be appropriate to update the risk assessment for DEHA (USEPA,
2002i). The literature search on reproductive and developmental
toxicity identified differences in the evaluation of the critical study
on which the MCLG is based. Therefore, EPA believes it is appropriate
to update the risk assessment and evaluate relevant new studies that
have become available on the toxicity of DEHA and its metabolites
including its potential developmental and reproductive toxicity. In
light of this information, EPA has initiated a reassessment of the
health risks resulting from exposure to DEHA and has already solicited
scientific information from the public for consideration (67 FR 1212,
January 9, 2002 (USEPA, 2002a)). Because the new assessment is not
expected to be completed until the 2003 or 2004 time frame, EPA does
not believe it is appropriate to revise the MCLG at this time.
The current MCL is not limited by the analytical or treatment
feasibility. Review of these capabilities is not necessary since no
changes to the MCL are warranted at this time. The results of EPA's
review of possible ``other regulatory revisions'' did not identify any
issues that are specific to DEHA (USEPA, 2002e). Because none of these
analyses indicate a change to the DEHA regulation, it is not necessary
to conduct a detailed occurrence and exposure analysis.
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for DEHA is appropriate at this time. A reassessment of the
health risks has been initiated and the Agency does not believe it is
appropriate to revise the NPDWR while that effort is in process.
29. Di(2-ethylhexyl)phthalate (DEHP)
a. Background. EPA published the current NPDWR for DEHP on July 17,
1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG of zero
based on a cancer classification of B2, probable human carcinogen, and
an MCL of 0.006 based on analytical feasibility.
b. Technical Reviews. The Agency has initiated a reassessment of
the health risks resulting from exposure to DEHP. Many studies on DEHP
and its metabolites have become available over the past decade and are
being evaluated as part of the Agency's ongoing assessment. The new
assessment will evaluate cancer and noncancer endpoints, including
potential developmental and reproductive endpoints. EPA expects the new
risk assessment to be completed in the 2002 or 2003 time frame (USEPA,
2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for DEHP is appropriate at this time because a reassessment
of the health risks resulting from exposure to DEHP is ongoing.
30. Dinoseb
a. Background. EPA published the current NPDWR for dinoseb on July
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG and
an MCL of 0.007 mg/L. The Agency developed the MCLG based on an RfD of
0.001 mg/kg/day and a cancer classification of D, not classifiable as
to human carcinogenicity.
b. Technical Reviews. The Agency has not updated the health risk
assessment for dinoseb since the NPDWR was published. Therefore, as
part of the Six-Year Review process, EPA conducted a literature search
for relevant data on the toxicology of dinoseb, including its potential
developmental and reproductive toxicity. The literature search did not
identify any studies that warrant a review of the RfD or the cancer
classification (USEPA, 2002i).
A review of analytical or treatment feasibility is not necessary
for dinoseb because changes to the MCLG are not warranted at this time,
and the current MCL is set at the MCLG. In addition, the results of
EPA's review of possible ``other regulatory revisions'' did not
identify any dinoseb-specific issues (USEPA, 2002e). Since EPA did not
identify a health or technology basis for revising the dinoseb NPDWR,
the Agency did not conduct a detailed occurrence and exposure analysis.
c. Preliminary Decision. After reviewing the results of the
pertinent technical analyses, the Agency believes the NPDWR for dinoseb
remains appropriate and thus, it is not subject to revision at this
time.
31. Diquat
a. Background. EPA published the current NPDWR for diquat on July
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG and
an MCL of 0.02 mg/L. The Agency developed the MCLG based on an RfD of
0.002 mg/kg/day and a cancer classification of D, not classifiable as
to human carcinogenicity.
b. Technical Reviews. The Agency has initiated a reassessment of
the health risks from exposure to diquat. The revised risk assessment
will consider relevant studies that have become available on the
toxicity of diquat, including its potential developmental and
reproductive toxicity. The Agency expects the new risk assessment to be
completed in the 2002 time frame (USEPA, 2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for diquat is appropriate at this time because a reassessment
of the health risks resulting from exposure to diquat is ongoing.
32. Endothall
a. Background. EPA published the current NPDWR for endothall on
July 17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an
MCLG and an MCL of 0.1 mg/L. The Agency developed the MCLG based on an
RfD of 0.02 mg/kg/day and a cancer classification of D, not
classifiable as to human carcinogenicity.
b. Technical Reviews. The Agency has initiated a reassessment of
the health risks resulting from exposure to endothall. The revised risk
assessment will consider relevant studies on the toxicity of endothall
including its potential developmental and reproductive toxicity. The
Agency expects the new risk assessment to be completed in the 2003 or
2004 time frame (USEPA, 2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for endothall is appropriate at this time because a
reassessment of the health risks resulting from exposure to endothall
is ongoing.
[[Page 19068]]
33. Endrin
a. Background. EPA published the current NPDWR for endrin on July
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG and
an MCL of 0.002 mg/L. The Agency developed the MCLG based on an RfD of
0.0003 mg/kg/day and a cancer classification of D, not classifiable as
to human carcinogenicity.
b. Technical Reviews. The Agency has not updated the health risk
assessment for endrin since the NPDWR was published; however, ATSDR
completed a toxicological profile for endrin in 1996 (ATSDR, 1996b).
This review did not find data that would warrant a review of the RfD or
cancer classification. As part of the Six-Year Review process, EPA
conducted a literature search for relevant data on the toxicology of
endrin, including its potential developmental and reproductive
toxicity. The literature search did not identify any studies that
warrant a review of the RfD or the cancer classification (USEPA,
2002i).
A review of analytical or treatment feasibility is not necessary
for endrin because changes to the MCLG are not warranted at this time
and the current MCL is set at the MCLG. In addition, the results of
EPA's review of possible ``other regulatory revisions'' did not
identify any endrin-specific issues (USEPA, 2002e). Since EPA did not
identify a health or technology basis for revising the endrin NPDWR,
the Agency did not conduct a detailed occurrence and exposure analysis.
(Note: Endrin uses were canceled in 1986 except for use on bird
perches, which was canceled in 1991 (USDA, 1998)).
c. Preliminary Decision. After reviewing the results of the
pertinent technical analyses, the Agency believes the NPDWR for endrin
remains appropriate and thus, it is not subject to revision at this
time.
34. Epichlorohydrin
a. Background. EPA published the current NPDWR for epichlorohydrin
on January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established
an MCLG of zero based on a cancer classification of B2, probable human
carcinogen. The NPDWR imposes a TT requirement that limits the
allowable level of epichlorohydrin monomer in the polymer that is added
to drinking water as a flocculent to remove particulates. Each water
system is required to certify, in writing, to the State (using third-
party or manufacturer's certification) that the combination (or
product) of dose and monomer level does not exceed the following level:
0.01 percent residual epichlorohydrin monomer in polymer products used
during water treatment and dosed at 20 ppm.
b. Technical Reviews. EPA has not identified any new information
that indicate that it is appropriate to revise the cancer
classification for epichlorohydrin at this time. Because the MCLG
remains at zero, the Agency believes that a further review of the
health effects of epichlorohydrin is not warranted at this time (USEPA,
2002i).
There are no standardized methods available for epichlorohydrin at
low levels in drinking water (56 FR 3526 at 3558, July 1, 1991 (USEPA,
1991a)). Therefore, no analysis of analytical feasibility is
appropriate for this contaminant. EPA has no new information that
indicates it is appropriate to revise the TT requirement for
epichlorohydrin at this time (USEPA, 2002k). The results of EPA's
review of possible ``other regulatory revisions'' did not identify any
issues which are specific to epichlorohydrin (USEPA, 2002e). Since EPA
did not identify a health or technology basis for revising the
epichlorohydrin NPDWR, the Agency did not conduct a detailed occurrence
and exposure analysis.
c. Preliminary Decision. After reviewing the results of the
pertinent technical analyses, the Agency believes the NPDWR for
epichlorohydrin remains appropriate and thus, it is not subject to
revision at this time.
35. Ethylbenzene
a. Background. EPA published the current NPDWR for ethylbenzene on
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an
MCLG and an MCL of 0.7 mg/L. The Agency developed the MCLG based on an
RfD of 0.1 mg/kg/day and a cancer classification of D, not classifiable
as to human carcinogenicity.
b. Technical Reviews. The Agency has initiated a reassessment of
the health risks resulting from exposure to ethylbenzene. The revised
risk assessment will consider relevant studies that have become
available on the toxicity of ethylbenzene, including its potential
developmental and reproductive toxicity. The Agency expects the new
risk assessment to be completed in the 2002 or 2003 time frame (USEPA,
2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for ethylbenzene is appropriate at this time because a
reassessment of the health risks resulting from exposure to
ethylbenzene is ongoing.
36. Ethylene Dibromide (EDB; 1,2-Dibromoethane)
a. Background. EPA published the current NPDWR for EDB on January
30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an MCLG of
zero based on a cancer classification of B2, probable human carcinogen.
The NPDWR also established an MCL of 0.00005 mg/L based on analytical
feasibility.
b. Technical Reviews. The Agency has initiated a reassessment of
the health risks resulting from exposure to EDB. The revised risk
assessment will consider relevant studies that have become available on
the toxicity of EDB, including its developmental and reproductive
toxicity. The Agency expects the new risk assessment to be completed in
the 2002 or 2003 time frame (USEPA, 2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for EDB is appropriate at this time because a reassessment of
the health risks resulting from exposure to EDB is ongoing.
37. Fluoride
a. Background. EPA published the current NPDWR for fluoride on
April 2, 1986 (51 FR 11396 (USEPA, 1986a)). The NPDWR established an
MCLG and an MCL of 4.0 mg/L. The MCLG was developed from a lowest
effect level for crippling skeletal fluorosis of 20 mg/day with
continuous exposures over a 20-year or longer period. The LOAEL was
divided by an uncertainty factor of 2.5 and a drinking water intake of
2 liters/day (L/day) to obtain the MCLG. Drinking water was considered
to be the only source of exposure for the calculation. At the same
time, EPA published a secondary maximum contaminant level (SMCL) for
fluoride of 2.0 mg/L to protect against dental fluorosis, which is
considered to be an adverse cosmetic effect. PWSs exceeding the
fluoride SMCL must provide public notification to their customers.
Fluoride is unique as a drinking water contaminant because of its
beneficial effects at low level exposures, and because it is
voluntarily added to some drinking water systems as a public health
measure for reducing the incidence of cavities among the treated
population. The amount of fluoride added to drinking water for
fluoridation ranges from 0.7 to 1.2 mg/L, depending on ambient air
temperatures. The decision to fluoridate a water supply is made by the
State or local municipality, and is not mandated by EPA or any other
Federal entity.
[[Page 19069]]
b. Technical Reviews. In 1997, NAS established Dietary Reference
Intakes (DRI) for fluoride as a nutrient. As a component of the DRI,
NAS established age and gender specific tolerable upper intake levels
(UL) to reflect the highest average daily nutrient intake level likely
to pose no risk of adverse effects to almost all individuals in the
general population. As intake increases above the UL, the potential
risk of adverse effects increases. The NAS set the UL for fluoride at
0.10 mg/kg/day for infants, toddlers, and children through eight years
of age, to protect them from moderate enamel fluorosis (NAS, 1997). A
UL of 10 mg/day was established for adults and for children older than
eight years, based on protection against skeletal fluorosis. The NAS UL
evaluation of fluoride does not have an effect on the MCLG/MCL because
a 2 liter drinking water intake of 4 mg/L equals 8mg/day for adults,
which is less than 10 mg/day and allows for fluoride in food and dental
products.
In addition, the NAS established age and gender specific Adequate
Intake (AI) values for fluoride. AI values are set when the data do not
permit determination of the more precise and better known Recommended
Dietary Allowance (RDA). The NAS (1997) AI for infants, 0 through 6
months, is 0.01 mg/day and for infants, 7 through 12 months, is 0.5 mg/
day. Values for children range from 0.7 mg/day to 3 mg/day increasing
with age. For adults, the NAS (1997) AI is 3 mg/day for females, and 4
mg/day for males.
There are new studies regarding the effects of fluoride on bone
that have been published since EPA established the MCLG/MCL. EPA
believes that it is important to review these new data, since effects
on bone are the basis of the present MCLG and MCL. The Agency has
conducted a literature search to identify reports of the clinical and
epidemiological data on fluoride and the skeletal system. The results
of that search indicate that a review of the new data is justified as
part of the regulatory review process. EPA plans to request NAS to
conduct a review of these data. In light of this planned assessment,
EPA does not believe it is appropriate to revise the MCLG at this time.
As part of the continuing review of the new toxicological data for
fluoride, EPA also intends to examine the RSC used in the 1986
regulation. At that time, a 100 percent RSC was applied in setting the
regulation. The increased use of fluoride in dental products, the
tendency for children to swallow these dental products, and the
potential for increased exposure from foods support a re-evaluation of
the RSC as a component of the fluoride review.
As a part of the review of possible ``other regulatory revisions,''
EPA identified one issue pertaining to the public notification
requirement associated with exceedance of the SMCL and the timing of
the notification. Currently, PWSs that exceed the SMCL of 2.0 mg/L are
required to notify their customers within 12 months of the exceedance.
Concern has been expressed that this requirement is not sufficiently
timely since dental fluorosis occurs as a result of exposure to high
levels of fluoride while the tooth enamel is being laid down. Waiting
12 months to provide public notification may result in young children
being exposed to high levels of fluoride during the time at which they
are most vulnerable. The Agency will consider any such revisions, if
they are still appropriate, once the results of the NAS evaluation are
available.
c. Preliminary Decision. EPA is continuing its analyses of relevant
studies that have been published since 1986 regarding the adverse
effects of fluoride on the skeletal system to determine if these data
support consideration of whether to revise the current MCLG. As a part
of this effort, the Agency plans to request that NAS update the
fluoride health risk assessment and review the RSC assumptions. The
Agency therefore believes it is not appropriate to revise the NPDWR for
fluoride at this time. When the results of the NAS assessment are
available, and if they support consideration of whether a revision to
the MCLG and/or MCL may be appropriate, EPA will revisit this ``not
revise'' decision.
38. Glyphosate
a. Background. EPA published the current NPDWR for glyphosate on
July 17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an
MCLG and an MCL of 0.7 mg/L. The Agency developed the MCLG based on an
RfD of 0.1 mg/kg/day and a cancer classification of D, not classifiable
as to human carcinogenicity.
b. Technical Reviews. The Agency has initiated a reassessment of
the health risks resulting from exposure to glyphosate. The revised
risk assessment will consider relevant studies that have become
available on the toxicity of glyphosate including its potential
developmental and reproductive toxicity. The Agency expects the new
risk assessment to be completed in the 2002 or 2003 time frame (USEPA,
2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for glyphosate is appropriate at this time because a
reassessment of the health risks resulting from exposure to glyphosate
is ongoing.
39. Heptachlor
a. Background. EPA published the current NPDWR for heptachlor on
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an
MCLG of zero based on a cancer classification of B2, probable human
carcinogen. The NPDWR also established an MCL of 0.0004 mg/L based on
analytical feasibility.
b. Technical Reviews. The Agency has not updated the health risk
assessment for heptachlor since the NPDWR was published; however, ATSDR
completed a toxicological profile for heptachlor in 1993 (ATSDR, 1993).
This assessment and other recent information do not warrant a review of
the cancer classification because there are inadequate data to support
a nonlinear dose-response relationship (USEPA, 2002i). Accordingly, the
MCLG remains at zero and the Agency believes that a further review of
the health effects of heptachlor is not warranted at this time.
The current MCL for heptachlor is based on a PQL of 0.0004 mg/L. As
a part of the Six-Year Review, EPA analyzed more recent WS data to
determine if it might be possible to recalculate the PQL (USEPA,
2002d). In addition, the Agency evaluated whether more sensitive
analytical methods have been approved and put into use by a wide number
of laboratories. The results of these analyses indicate that some
improvement in analytical feasibility might exist. Evaluation of the WS
data shows that EPA Regional and State laboratories exhibit greater
than 90 percent laboratory passing rates at concentrations around the
current PQL of 0.0004 mg/L. Because most of the laboratory passing
rates exceeded the 75 percent criterion typically used to derive a PQL
from WS studies, this information indicates that a lower PQL
corresponding to the 75 percent passing rate might exist for
heptachlor. While this information is indicative of a possibly lower
PQL, the WS data are insufficient at this time to actually recalculate
what the lower PQL for heptachlor might be.
Using information about the analytical methods most widely used to
report results in the WS studies, the MDLs for these methods, and the
10 times MDL multiplier, EPA estimated what the possibly lower PQL/MCL
might be. For the analysis of heptachlor in the more recent WS studies,
[[Page 19070]]
laboratories predominantly used EPA Methods 508 (GC/MS), 505 (GC
microextraction), and 525.2 (Purge and Trap GC), which have MDLs of
0.0000015 mg/L, 0.000003 mg/L, and 0.00015 mg/L, respectively. A 10
times MDL multiplier predicts PQLs of 0.000015 mg/L, 0.00003 mg/L, and
0.0015 mg/L. EPA chose the intermediate value, rounded up to 0.0001 mg/
L, and used this value as a threshold in the occurrence analysis
discussed in this section.
Since the analytical feasibility analysis indicates that the PQL
for heptachlor (and therefore the MCL) could possibly be lower if EPA
had more definitive data to recalculate the PQL, EPA considered whether
treatment feasibility is likely to pose any limitations (USEPA, 2002k).
The current BAT for heptachlor is GAC. Compliance technologies for
small systems include GAC, PAC, and POU GAC. Since heptachlor is a
moderately adsorbed contaminant, EPA believes that the BAT and
compliance technologies are still practical and would not pose any
limitations for heptachlor at a possibly lower MCL.
The results of EPA's review of possible ``other regulatory
revisions'' did not identify any heptachlor-specific issues (USEPA,
2002e).
EPA evaluated the results of the occurrence and exposure analyses
for heptachlor to determine whether changes to the MCL might be
appropriate and likely to result in additional public health protection
if the PQL were recalculated (USEPA, 2002g; USEPA, 2002h). Table V-9
shows the results of the detailed occurrence and exposure analyses
based on the 16-State cross-section for the current MCL (0.0004 mg/L)
and the possible PQL/MCL based on the analytical feasibility analysis
(0.0001 mg/L).
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Based on the detailed occurrence and exposure analysis, heptachlor
is unlikely to occur at the current MCL or any potential MCL revision
for the States used in the cross-section. Since all heptachlor uses
were canceled in the United States in 1988 (except for fire ant use),
and since it is subject to the United Nations Prior Informed Consent
procedure (USEPA, 2002g; USEPA, 2002h), EPA expects the occurrence of
heptachlor in PWSs to be rare.
c. Preliminary Decision. Although there are new data that support
consideration of a slightly lower PQL (and therefore a possibly lower
MCL), EPA does not believe a revision to the NPDWR for heptachlor is
appropriate at this time. The Agency does not have sufficient data at
this time on which to base a PQL recalculation and hence an MCL
revision. Also, the Agency believes that any change in the PQL would be
minimal and unlikely to significantly improve the level of public
health protection because heptachlor appears to occur very infrequently
at concentrations at or below the current MCL.
[[Page 19071]]
40. Heptachlor Epoxide
a. Background. EPA published the current NPDWR for heptachlor
epoxide, a degradate of heptachlor, on January 30, 1991 (56 FR 3526
(USEPA, 1991a)). The NPDWR established an MCLG of zero based on a
cancer classification of B2, probable human carcinogen. The NPDWR also
established an MCL of 0.0002 mg/L based on analytical feasibility.
b. Technical Reviews. The Agency has not updated the health risk
assessment for heptachlor epoxide since the NPDWR was published;
however, ATSDR completed a toxicological profile for heptachlor epoxide
in 1993 (ATSDR, 1993). This review did not find data that would warrant
a review of the cancer classification because there are inadequate data
to support a nonlinear dose response. Accordingly, the MCLG remains at
zero and the Agency believes that a further review of the health
effects of heptachlor epoxide is not warranted at this time.
The current MCL for heptachlor epoxide is based on a PQL of 0.0002
mg/L. As a part of the Six-Year Review, EPA analyzed more recent WS
data to determine if it might be possible to recalculate the PQL
(USEPA, 2002d). In addition, the Agency evaluated whether more
sensitive analytical methods have been approved and put into use by a
wide number of laboratories. The results of these analyses indicate
that a slight improvement in analytical feasibility might exist.
Evaluation of the WS data shows that EPA Regional and State
laboratories exhibit greater than 85 percent laboratory passing rates
at concentrations around the current PQL of 0.0002 mg/L. Because most
of the laboratory passing rates exceeded the 75 percent criterion
typically used to derive a PQL from WS studies, this information
indicates that a lower PQL corresponding to the 75 percent passing rate
might exist for heptachlor epoxide. While this information is
indicative of a possibly lower PQL, the WS data are insufficient at
this time to actually recalculate what the lower PQL for heptachlor
epoxide might be.
Using information about the analytical methods most widely used to
report results in the WS studies, the MDLs for these methods, and the
10 times MDL multiplier, EPA estimated what the possibly lower PQL/MCL
might be. For the analysis of heptachlor epoxide in the more recent WS
studies, laboratories predominantly used EPA Methods 505 (GC
microextraction), 508 (GC/MS), and 525.2 (Purge and Trap GC), which
have MDLs of 0.000004 mg/L, 0.0000059 mg/L, and 0.00013 mg/L,
respectively. A 10 times MDL multiplier predicts PQLs of 0.00004 mg/L,
0.000059 mg/L, and 0.0013 mg/L. EPA chose the intermediate value,
rounded up to 0.0001 mg/L, and used this value as a threshold in the
occurrence analysis discussed in this section.
Since the analytical feasibility analysis indicates that the PQL
for heptachlor epoxide (and therefore the MCL) could possibly be lower
if EPA had more definitive data to recalculate the PQL, EPA considered
whether treatment feasibility is likely to pose any limitations (USEPA,
2002k). The current BAT for heptachlor epoxide is GAC. Compliance
technologies for small systems include GAC, PAC, and POU GAC. EPA
believes that the BAT and compliance technologies would not pose any
limitations for heptachlor epoxide at a possibly lower MCL.
The results of EPA's review of possible ``other regulatory
revisions'' did not identify any issues that are specific to heptachlor
epoxide (USEPA, 2002e).
EPA evaluated the results of the occurrence and exposure analyses
for heptachlor epoxide to determine whether changes to the MCL might be
appropriate and likely to result in additional public health protection
if the PQL were recalculated (USEPA, 2002g; USEPA, 2002h). Table V-10
shows the results of the detailed occurrence and exposure analyses
based on the 16-State cross-section for the current MCL (0.0002 mg/L),
and the possible PQL/MCL based on the analytical feasibility analysis
(0.0001 mg/L).
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[[Page 19072]]
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BILLING CODE 6560-50-C
Based on detailed occurrence and exposure analysis, it appears that
heptachlor epoxide is unlikely to occur at the current MCL or any
potential MCL revision for the States used in the cross-section. Since
the parent of heptachlor epoxide (i.e., heptachlor) was canceled for
use (except for fire ant use) in the United States and since it is
subject to the United Nations Prior Informed Consent procedure (USEPA,
2002g; USEPA, 2002h), EPA expects the occurrence of heptachlor epoxide
in PWSs to be rare.
c. Preliminary Decision. Although there are new data that support
consideration of a slightly lower PQL (and therefore a possibly lower
MCL), EPA does not believe a revision to the NPDWR for heptachlor
epoxide is appropriate at this time. The Agency does not have
sufficient data at this time on which to base a PQL recalculation and
hence an MCL revision. Also, the Agency believes that any change in the
PQL would be minimal and unlikely to significantly improve the level of
public health protection because heptachlor epoxide appears to occur
infrequently at concentrations at or below the current MCL.
41. Hexachlorobenzene
a. Background. EPA published the current NPDWR for
hexachlorobenzene on July 17, 1992 (57 FR 31776 (USEPA, 1992)). The
NPDWR established an MCLG of zero based on a cancer classification of
B2, probable human carcinogen. The NPDWR also established an MCL of
0.001 mg/L based on analytical feasibility.
b. Technical Reviews. The Agency has not updated the health risk
assessment for hexachlorobenzene since the NPDWR was published;
however, ATSDR completed a toxicological profile for hexachlorobenzene
in 1996 (ATSDR, 1996c). This assessment and other recent information do
not warrant a review of the cancer classification because there are
inadequate data to support a nonlinear dose-response relationship
(USEPA, 2002i). Accordingly, the MCLG remains at zero and the Agency
believes that a further review of the health effects of
hexachlorobenzene is not warranted at this time.
The current MCL for hexachlorobenzene is based on a PQL of 0.001
mg/L. As a part of the Six-Year Review, EPA analyzed more recent WS
data to determine if it might be possible to recalculate the PQL
(USEPA, 2002d). In addition, the Agency evaluated whether more
sensitive analytical methods have been approved and put into use by a
wide number of laboratories. The results of these analyses indicate
that some improvement in analytical feasibility might exist. Evaluation
of the WS data shows that EPA Regional and State laboratories exhibit
greater than 90 percent laboratory passing rates at concentrations
around the current PQL of 0.001 mg/L. Because most of the laboratory
passing rates exceeded the 75 percent criterion typically used to
derive a PQL from WS studies, this information indicates that a lower
PQL corresponding to the 75 percent passing rate might exist for
hexachlorobenzene. While this information is indicative of a possibly
lower PQL, the WS data are insufficient at this time to actually
[[Page 19073]]
recalculate what the lower PQL for hexachlorobenzene might be.
Using information about the analytical methods most widely used to
report results in the WS studies, the MDLs for these methods, and the
10 times MDL multiplier, EPA estimated what the possibly lower PQL/MCL
might be. For the analysis of hexachlorobenzene in the more recent WS
studies, laboratories predominantly used EPA Methods 508 (GC/MS), 505
(GC microextraction), and 525.2 (Purge and Trap GC), which have MDLs of
0.0000077 mg/L, 0.000002 mg/L and 0.000001 mg/L, respectively. A 10
times MDL multiplier predicts PQLs of 0.000077 mg/L, 0.00002 mg/L, and
0.00001 mg/L. EPA chose the highest value, rounded up to 0.0001 mg/L,
and then used this value as a threshold in the occurrence analysis
discussed in this section.
Since the analytical feasibility analysis indicates that the PQL
for hexachlorobenzene (and therefore the MCL) could possibly be lower
if EPA had more definitive data to recalculate the PQL, EPA considered
whether treatment feasibility is likely to pose any limitations (USEPA,
2002k). The current BAT for hexachlorobenzene is GAC. Compliance
technologies for small systems include GAC, PAC, and POU GAC. Since
hexachlorobenzene is a moderately adsorbed contaminant, EPA believes
that the BAT and compliance technologies are still practical and would
not pose any limitations for hexachlorobenzene at a possibly lower MCL.
The results of EPA's review of possible ``other regulatory
revisions'' did not identify any issues that are specific to
hexachlorobenzene (USEPA, 2002e).
EPA evaluated the results of the occurrence and exposure analyses
for hexachlorobenzene to determine whether changes to the MCL might be
appropriate and likely to result in additional public health protection
if the PQL were recalculated (USEPA, 2002g; USEPA, 2002h). Table V-11
shows the results of the detailed occurrence and exposure analyses
based on the 16-State cross-section for the current MCL (0.001 mg/L)
and the possible PQL/MCL based on the analytical feasibility analysis
(0.0001 mg/L).
BILLING CODE 6560-50-P
[GRAPHIC] [TIFF OMITTED] TP17AP02.020
BILLING CODE 6560-50-C
The detailed occurrence and exposure analysis indicates that
hexachlorobenzene is unlikely to occur at the current MCL or any
potential MCL revision for the States used in the cross-section. Since
hexachlorobenzene
[[Page 19074]]
uses were canceled in the United States in 1984 and since it is subject
to the United Nations Prior Informed Consent procedure (USEPA, 2002g;
USEPA, 2002h), EPA expects the occurrence of hexachlorobenzene in PWSs
to be rare.
c. Preliminary Decision. Although there are new data that support
consideration of a possibly lower PQL (and therefore a possibly lower
MCL), EPA does not believe a revision to the NPDWR for
hexachlorobenzene is appropriate at this time. The Agency does not have
sufficient data at this time on which to base a PQL recalculation and
hence an MCL revision. In addition, because the occurrence of
hexachlorobenzene appears to be minimal between the current MCL and any
likely PQL/MCL revision, the Agency believes that any potential
revisions to the hexachlorobenzene NPDWR are unlikely to significantly
improve the level of public health protection.
42. Hexachlorocyclopentadiene
a. Background. EPA published the current NPDWR for
hexachlorocyclopentadiene on July 17, 1992 (57 FR 31776 (USEPA, 1992)).
The NPDWR established an MCLG and an MCL of 0.05 mg/L. The Agency based
the MCLG on an RfD of 0.007 mg/kg/day and a cancer classification of D,
not classifiable as to human carcinogenicity.
b. Technical Reviews. The Agency updated the health risk assessment
for hexachlorocyclopentadiene in 2001 (USEPA, 2001c). The revised risk
assessment considered relevant studies that were available to the
Agency on the toxicity of hexachlorocyclopentadiene including its
potential developmental and reproductive toxicity. According to the
1986 EPA Guidelines for Carcinogen Risk Assessment (51 FR 33992,
September 24, 1986 (USEPA, 1986b)), evaluation of the weight of
evidence for carcinogenicity to humans indicates that
hexachlorocyclopentadiene is most appropriately categorized as Group E,
evidence of noncarcinogenicity to humans, via inhalation exposure. In
accordance with EPA's 1996 Proposed Guidelines for Carcinogen Risk
Assessment (61 FR 17960, April 23, 1996 (USEPA, 1996)),
hexachlorocyclopentadiene is not likely to be a human carcinogen by the
inhalation route. The potential for carcinogenicity by the oral route
is unknown. The updated risk assessment changed the RfD from 0.007 to
0.006 mg/kg/day. The change in RfD was the result of a change in the
procedure used to model the data but not a change in the underlying
toxicology. The RfD could result in a slight change to the MCLG and MCL
but that change would not lead to any significant improvement in public
health protection.
A review of analytical or treatment feasibility is not necessary
for hexachlorocyclopentadiene because changes to the MCLG are not
warranted at this time and the current MCL is set at the MCLG. In
addition, the results of EPA's review of possible ``other regulatory
revisions'' did not identify any hexachlorocyclopentadiene-specific
issues (USEPA, 2002e). Since EPA did not identify a health or
technology basis for revising the hexachlorocyclopentadiene NPDWR, the
Agency did not conduct a detailed occurrence and exposure analysis.
c. Preliminary Decision. After reviewing the results of the
pertinent technical analyses, the Agency believes the NPDWR for
hexachlorocyclopentadiene remains appropriate and thus, it is not
subject to revision at this time.
43. Lead
a. Background. EPA published the current NPDWR for lead on June 7,
1991 (56 FR 26460 (USEPA, 1991b)). The NPDWR established an MCLG of
zero and a lead action level of 0.015 mg/L at the 90th percentile of
taps tested. The MCLG for lead is based on three factors: (1) the
occurrence of a variety of low level health effects for which it is
currently difficult to identify clear threshold exposure levels below
which there are no risks of adverse health effects; (2) the Agency's
policy goal that drinking water should contribute minimal lead to total
lead exposures because a substantial portion of the sensitive
population already exceeds acceptable blood lead levels; and (3) the
classification of lead as B2, probable human carcinogen.
The NPDWR requires water systems to monitor for lead at the tap.
Water systems must optimize corrosion control. This requires water
systems serving more than 50,000 persons (except those with extremely
low levels of lead in their distribution systems) and those smaller
size systems that exceed the lead action level to install corrosion
control treatment and to monitor for specified water quality control
parameters. The NPDWR also includes other TT requirements for those
systems exceeding the lead action level. These systems must: (1)
Monitor for lead in source water; (2) install source water treatment,
if appropriate; (3) conduct public education for as long as they
continue to exceed the action level; and (4) replace the portion of
lead service line in the distribution system they own, if they continue
to exceed the action level after installing corrosion control treatment
and/or source water treatment. EPA published revisions to the lead
NPDWR on January 12, 2000 (65 FR 1950 (USEPA, 2000a)). These revisions
made changes to monitoring and reporting requirements, public
education, and the lead service line replacement requirements but did
not affect the lead MCLG, action level, or other TT requirements.
b. Technical Reviews. EPA has not identified any new assessments
that indicate that it is appropriate to revise the MCLG for lead at
this time (USEPA, 2002i). Although ATSDR completed a toxicological
profile for lead in 1999 (ATSDR, 1999), the review did not find data
that would warrant a change in the MCLG for lead. Because the MCLG
remains at zero, the Agency believes that a further review of the
health effects of lead is not warranted at this time.
EPA identified several potential research needs which may be
considered in the context of an overall drinking water research
strategy. These research needs are described in the ``Water Treatment
Technology Feasibility Support Document of Chemical Contaminants in
Support of EPA Six-Year Review of National Primary Drinking Water
Regulations'' (USEPA, 2002k).
Some stakeholders have suggested that EPA allow alternatives to
corrosion control treatment (e.g., monitoring and flushing at non-
transient, non-community water systems (NTNCWSs)) (USEPA, 2002e). EPA
considered these alternatives as a part of the January 2000 revisions
and determined that it was not appropriate to make such revisions to
the TT requirements for lead and copper (65 FR 1950, January 12, 2000
(USEPA, 2000a)). If new peer-reviewed scientific information becomes
available, it will be considered.
EPA also considered several potential revisions to requirements
pertaining to the monitoring requirements for lead and copper in
drinking water based on concerns recently expressed by stakeholders
(USEPA, 2002e). As a part of the Six-Year Review process, EPA
considered issues including: (1) Further reduction of the monitoring
requirements; (2) monitoring for lead and copper on the same frequency
as other inorganic and organic chemicals; (3) expanding the monitoring
waiver program to water systems that have not exceeded one-half the
lead and copper action levels for three monitoring rounds, regardless
of plumbing materials used; (4) revising the protocol by which tap
water sampling sites are identified; and (5) allowing fewer than five
tap water samples for NTNCWSs
[[Page 19075]]
that have fewer than five taps. The Agency addressed all of these
issues as a part of the January 2000 revisions. If new peer-reviewed
scientific information becomes available, it will be considered.
The current action level and TT requirements are not limited by
analytical feasibility, therefore review of these capabilities is not
needed. Since none of the analyses indicate a change to the lead
regulation at this time, the Agency did not conduct detailed occurrence
and exposure analyses.
c. Preliminary Decision. EPA does not believe a revision to the
NPDWR for lead is appropriate because the Agency is not aware of any
new data/information that provides sufficient basis for revising the
regulatory requirements at this time. However, the Agency has
identified several technology-related issues that could benefit from
further research. These research needs will be considered as a part of
an overall drinking water research strategy. As more research in this
area becomes available, the Agency will consider the results as a part
of the review of the lead NPDWR during future review cycles.
44. Lindane (-Hexachlorocyclohexane)
a. Background. EPA published the current NPDWR for lindane on
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an
MCLG and an MCL of 0.0002 mg/L. The Agency based the MCLG on an RfD of
0.0003 mg/L and a cancer classification of C, possible human
carcinogen.
b. Technical Reviews. The Agency has initiated a reassessment of
the health risks resulting from exposure to lindane. The revised risk
assessment will consider relevant studies that have become available on
the toxicity of lindane including its potential developmental and
reproductive toxicity. The Agency expects the new risk assessment to be
completed in the 2003 or 2004 time frame (USEPA, 2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for lindane is appropriate at this time because a
reassessment of the health risks resulting from exposure to lindane is
ongoing.
45. Mercury (Inorganic)
a. Background. EPA published the current NPDWR for inorganic
mercury on January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR
established an MCLG and an MCL of 0.002 mg/L. The Agency based the MCLG
on a Drinking Water Equivalent Level (DWEL) of 0.01 mg/L \10\ and a
cancer classification of D, not classifiable as to human
carcinogenicity.
---------------------------------------------------------------------------
\10\ The DWEL was recommended by a panel of experts on mercury,
and was derived using the weight of evidence from the entire
inorganic mercury database. The DWEL was later back-calculated to an
RFD of 0.0003 mg/kg/day (USEPA, 1995).
---------------------------------------------------------------------------
b. Technical Reviews. EPA updated the risk assessment for mercury
in 1997 as part of the Mercury Study Report to Congress (MSRC) (USEPA,
1997b). The MSRC entailed a review of all available studies on
inorganic mercury including reproductive and developmental studies. The
MSRC concluded that the database for inorganic mercury is suggestive of
effects in animals at doses around 2 mg/kg/day. The data however, are
considered insufficient for risk assessment based on any single study
or on the database as a whole. Evaluation of data for germ cell
mutagenicity led to the conclusion that there is a moderate weight of
evidence for potential to produce adverse effects in humans. The MSRC
reviewed and kept the 1987 RfD of 0.0003 mg/kg/day based on immune-
mediated kidney damage in three studies conducted in a sensitive strain
of rats.
The MSRC evaluated data for carcinogenicity of inorganic mercury,
largely from studies of mercuric chloride. Based on the absence of
human data and limited data in animals, inorganic mercury was
categorized as Group C, possible human carcinogen; this determination
was posted on IRIS for mercuric chloride (USEPA, 1995). The MSRC also
applied the proposed revisions to the Cancer Guidelines (61 FR 17960,
April 23, 1996 (USEPA, 1996)) to the evaluation of inorganic mercury.
The conclusion was that inorganic mercury is not likely to be a human
carcinogen under conditions of exposure generally encountered in the
environment. This was based in part on the observation that all tumors
were observed at very high doses, in excess of the maximum tolerated
dose (MTD) and that likely modes of action for these tumors involved
irritation and cytotoxic effects not expected to occur at environmental
levels.
The revised risk assessments show that inorganic mercury is not
likely to be a carcinogen at levels found in water and that there are
insufficient data to categorize inorganic mercury as a developmental
toxicant. The EPA RfD has not changed, and thus, EPA does not believe
it is appropriate to revise the MCLG at this time.
A review of analytical or treatment feasibility is not necessary
for mercury because, in EPA's judgment, changes to the MCLG are not
warranted at this time and the current MCL is set at the MCLG. In
addition, the results of EPA's review of possible ``other regulatory
revisions'' did not identify any mercury-specific issues (USEPA,
2002e). Since EPA did not identify a health or technology basis for
revising the mercury NPDWR, the Agency did not conduct a detailed
occurrence and exposure analysis.
c. Preliminary Decision. After reviewing the results of the
pertinent technical analyses, the Agency believes the NPDWR for
inorganic mercury remains appropriate and thus, it is not subject to
revision at this time.
46. Methoxychlor
a. Background. EPA published the current NPDWR for methoxychlor on
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an
MCLG and an MCL of 0.04 mg/L. The Agency based the MCLG on an RfD of
0.005 mg/kg/day and a cancer classification of D, not classifiable as
to human carcinogenicity.
b. Technical Reviews. The Agency has initiated a reassessment of
the health risks resulting from exposure to methoxychlor. The revised
risk assessment will consider relevant studies that have become
available on the toxicity of methoxychlor including its potential
developmental and reproductive toxicity. The Agency expects the new
risk assessment to be completed in the 2002 or 2003 time frame (USEPA,
2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for methoxychlor is appropriate at this time because a
reassessment of the health risks resulting from exposure to
methoxychlor is ongoing.
47. Monochlorobenzene (Chlorobenzene)
a. Background. EPA published the current NPDWR for
monochlorobenzene on January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The
NPDWR established an MCLG and an MCL of 0.1 mg/L. The Agency based the
MCLG on an RfD of 0.02 mg/kg/day and a cancer classification of D, not
classifiable as to human carcinogenicity.
b. Technical Reviews. The Agency has not updated the health risk
assessment for monochlorobenzene since the NPDWR was published. EPA
therefore conducted a literature search for relevant studies on the
toxicology of monochlorobenzene including its potential developmental
and reproductive toxicity as a part of the Six-Year Review process. The
literature search did not identify any new studies
[[Page 19076]]
that warrant a review of the RfD or the cancer classification (USEPA,
2002i).
A review of analytical or treatment feasibility is not necessary
for monochlorobenzene because changes to the MCLG are not warranted at
this time and the current MCL is set at the MCLG. In addition, the
results of EPA's review of possible ``other regulatory revisions'' did
not identify any monochlorobenzene-specific issues (USEPA, 2002e).
Since EPA did not identify a health or technology basis for revising
the monochlorobenzene NPDWR, the Agency did not conduct a detailed
occurrence and exposure analysis.
c. Preliminary Decision. After reviewing the results of the
pertinent technical analyses, the Agency believes the NPDWR for
monochlorobenzene remains appropriate and thus, it is not subject to
revision at this time.
48. Nitrate (as N)
a. Background. EPA published the current NPDWR for nitrate on
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an
MCLG and MCL of 10 mg/L (as nitrogen (N)). The Agency based the MCLG on
an RfD of 1.6 mg/kg/day (as N) and a cancer classification of D, not
classifiable as to human carcinogenicity.
b. Technical Reviews. The current RfD and the MCLG were established
to protect infants, the most susceptible segment of the population. At
the request of EPA \11\, NAS completed an assessment of nitrate in 1995
(NAS, 1995) and did not find any new data that would warrant a review
of the RfD or cancer classification. The literature search conducted
during the Six-Year Review also did not identify any new studies that
warrant a review of the RfD or cancer classification (USEPA, 2002i).
---------------------------------------------------------------------------
\11\ This request fulfilled the commitment EPA made to form an
inter-agency workgroup to determine what, if any, oncogenic risks
exist (56 FR 3526 at 3538, January 30th, 1991 (USEPA, 1991a)).
---------------------------------------------------------------------------
The current MCL is not limited by the analytical or treatment
feasibility. Review of these capabilities is not necessary since no
changes to the MCL are warranted at this time.
As a part of the Six-Year Review, several States have suggested
that EPA revise the current monitoring requirements for nitrate to
allow less frequent monitoring in systems with consistently low
nitrate/nitrite levels. Some have suggested that EPA place nitrate
monitoring under the same monitoring framework used for most other
inorganic chemicals (USEPA, 2002e). EPA previously considered these
suggestions when the Agency considered chemical monitoring reform and
decided not to change the frequency of nitrate monitoring. However,
primacy agencies currently have the flexibility to reduce nitrate
monitoring for ground water systems from annually to biennial if the
Primacy Agency adopts (and EPA approves) an alternative monitoring
provision. EPA has established guidance for such alternative monitoring
in the Alternative Monitoring Guidelines (USEPA, 1997a). These
guidelines were issued after consultation with stakeholders and no new
information has been identified that warrants reconsideration of this
issue.
Detailed occurrence and exposure analysis is not necessary since
none of the analyses indicate a change to the nitrate regulation at
this time.
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for nitrate is appropriate at this time because: (1) There
are no changes in the health risk assessment for nitrate; and (2) no
other new data were identified that indicate the need to revise the
NPDWR at this time. (Also see section V.A.49.c of today's action for a
discussion of the Agency's decision pertaining to the joint nitrate/
nitrite standard.)
49. Nitrite (as N)
a. Background. EPA published the current NPDWR for nitrite on
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an
MCLG and an MCL of 1.0 mg/L (as N). The Agency based the MCLG on an RfD
of 0.16 mg/kg/day (as N) and a cancer classification of D, not
classifiable as to human carcinogenicity.
b. Technical Reviews. The current RfD and MCLG were established to
protect infants, the most susceptible segment of the population. At the
request of EPA, NAS completed an assessment of nitrite in 1995 (NAS,
1995) and did not find any new studies that warrant a review of the RfD
or cancer classification. The literature search conducted during the
Six-Year Review did not identify any new studies that warrant a review
of the RfD or the cancer classification (USEPA, 2002i).
The current MCL is not limited by the analytical or treatment
feasibility. Review of these capabilities is not necessary since no
changes to the MCL are warranted at this time.
As a part of the Six-Year Review of ``other regulatory revisions,''
EPA received several suggestions regarding the current monitoring
requirements for nitrite.\12\ Stakeholders raised several potential
issues concerning the current monitoring requirements (USEPA, 2002e).
These issues include:
---------------------------------------------------------------------------
\12\ Current monitoring requirements for nitrite: All community
water systems (CWSs), non-transient, non-community water systems
(NTNCWSs), and transient non-community water systems (TNCWSs) must
monitor for nitrite at each entry point to the distribution system.
If the analytical result is less than \1/2\ the MCL (0.5 mg/L), then
the system must monitor at a frequency specified by the Primary
Agency. If the sample result is greater than or equal to \1/2\ the
MCL (0.5 mg/L) then the entry point that exceeded the trigger level
must begin quarterly monitoring. The Primary Agency may reduce the
quarterly monitoring to annual monitoring after the system has
collected four quarters of data. However, the system must collect
subsequent samples during the quarter that yielded the highest
analytical result.
---------------------------------------------------------------------------
A need for flexibility for States to require systems to
collect a distribution system sample for nitrite under certain
circumstances, such as if the entry point sample is greater than 50
percent of the MCL, if there is a large amount of ammonia in the raw
water, or if chloramines are applied;
A need for flexibility for States to require systems to
monitor for ammonia in raw water; and
Flexibility to eliminate nitrite monitoring when a
disinfection residual is present.
EPA does not believe it has sufficient data at this time on which
to base possible changes in monitoring requirements (USEPA, 2002e).
Detailed occurrence and exposure analysis is not necessary since
none of the technical analyses indicate a change to the nitrite
regulation at this time.
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for nitrite is appropriate at this time because: (1) There
are no changes in the health risk assessment for nitrite; and (2) no
other new data were identified that indicate the need to revise the
NPDWR at this time.
EPA also published an MCLG and an MCL of 10 mg/L (as N) for the sum
of nitrate and nitrite on January 30, 1991 (56 FR 3526 (USEPA, 1991a)).
The Agency established this joint nitrate/nitrite standard to account
for the possible additive toxicity of these two chemicals and also to
protect against the deterioration of drinking water quality, since the
presence of nitrite in water is indicative of water contaminated with
sewage. The Agency has not identified any new data as a part of the
Six-Year Review process that indicates that this joint nitrate/nitrite
standard needs to be revised.
50. Oxamyl (Vydate)
a. Background. EPA published the current NPDWR for oxamyl on July
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG and
an MCL of 0.2 mg/L. The Agency based the
[[Page 19077]]
MCLG on an RfD of 0.025 mg/kg/day and a cancer classification of E,
evidence of non-carcinogenicity for humans.
b. Technical Reviews. The Agency identified a change in the health
assessment that supports consideration of whether to revise the MCLG
(USEPA, 2002i). EPA updated the risk assessment in 2000. This new risk
assessment considered relevant studies that had become available on the
toxicity of oxamyl including its potential developmental and
reproductive toxicity. The new risk assessment revised the RfD from
0.025 mg/kg/day to 0.001 mg/kg/day (USEPA, 2000e).
Based on the change in the RfD for oxamyl and using a 20 percent
RSC \13\, EPA believes that any revision to the MCLG is not likely to
be lower than 0.007 mg/L.
---------------------------------------------------------------------------
\13\ This is the RSC used for the current MCLG and also the
default value. EPA has no reason to believe that the RSC for oxamyl
would change. See Appendix A for further discussion of the RSC.
---------------------------------------------------------------------------
In setting the MCLG/MCL in 1992, the Agency determined the PQL for
oxamyl to be 0.02 mg/L and analytical feasibility was not considered to
be a limitation. EPA has analyzed more recent WS data to determine if
analytical feasibility is likely to be a limiting factor in setting a
lower MCL (USEPA, 2002d). In addition, the Agency evaluated whether
more sensitive methods have been approved and are in use by a wide
number of laboratories. The results of these analyses indicate that
analytical feasibility is likely to be a limiting factor if EPA were to
revise the MCLG and MCL. Although not definitive, the available WS data
indicate that the PQL could lie between 0.02 and 0.04 mg/L. EPA used
the 0.02 mg/L and the 0.04 mg/L values as thresholds in the occurrence
analysis discussed in this section.
Since the health effects technical review supports consideration of
whether a revision to the MCLG and MCL may be appropriate, EPA
evaluated whether treatment feasibility is likely to pose any
limitations (USEPA, 2002k). The current BAT for oxamyl is GAC.
Compliance technologies for small systems include GAC, PAC, and POU
GAC. EPA believes that the BAT and compliance technologies are still
practical and would not pose any limitations for oxamyl at a possibly
lower level (i.e., a possibly lower MCL).
The results of EPA's review of possible ``other regulatory
revisions'' did not identify any issues that are specific to oxamyl
(USEPA, 2002e).
EPA evaluated the results of the occurrence and exposure analyses
for oxamyl to determine whether changes to the MCL might be appropriate
and likely to result in additional public health protection if the PQL
were recalculated (USEPA, 2002g; USEPA, 2002h). Table V-12 shows the
results of the detailed occurrence and exposure analyses based on the
16-State cross-section for several concentrations: the current MCL (0.2
mg/L), the possible upper and lower PQLs based on the analytical
feasibility analysis (0.02 and 0.04 mg/L), and the possible lower limit
of any MCLG value (0.007 mg/L). Based on the detailed analysis of 16
cross-section States, it appears that oxamyl is unlikely to occur at
the current MCL or any potential MCL value.
BILLING CODE 6560-50-P
[[Page 19078]]
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BILLING CODE 6560-50-C
c. Preliminary Decision. Although there are new data indicating
that it might be possible to lower the MCLG and the MCL, analytical
feasibility limitations would limit the extent to which the MCL could
be revised at the present time. Because any changes in the NPDWR based
on setting the MCL at the limitations of analytical feasibility are
unlikely to significantly improve the level of public health
protection, EPA does not believe a revision to the NPDWR for oxamyl is
appropriate at this time. In addition, because oxamyl appears to occur
infrequently at concentrations at or below the current MCL, EPA
believes that efforts to research more sensitive analytical methods
and/or to revise the MCL are low priority and should not be pursued at
the present time. EPA requests comment on the extent to which oxamyl is
likely to occur at levels between 0.007 and 0.2 mg/L at PWSs.
Commenters who disagree with the occurrence evaluation should submit
data to support their rationale and evidence to show that oxamyl is of
national concern at PWSs at the thresholds evaluated. EPA does plan to
update the Health Advisory for oxamyl to reflect the new RfD.
51. Pentachlorophenol
a. Background. EPA published the current NPDWR for
pentachlorophenol on July 1, 1991 (56 FR 30266 (USEPA, 1991c)). The
NPDWR established an MCLG of zero based on a cancer classification of
B2, probable human carcinogen. The NPDWR also established an MCL of
0.001 mg/L, based on analytical feasibility.
b. Technical Reviews. The Agency has initiated a reassessment of
the health risks resulting from exposure to pentachlorophenol. The
revised risk assessment will consider relevant studies that have become
available on the toxicity of pentachlorophenol
[[Page 19079]]
including its potential developmental and reproductive toxicity. The
Agency expects the new risk assessment to be completed in the 2002 or
2003 time frame (USEPA, 2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for pentachlorophenol is appropriate at this time because a
reassessment of the health risks resulting from exposure to
pentachlorophenol is ongoing.
52. Picloram
a. Background. EPA published the current NPDWR for picloram on July
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG and
an MCL of 0.5 mg/L. The Agency based the MCLG on an RfD of 0.07 mg/kg/
day and a cancer classification of D, not classifiable as to human
carcinogenicity.
b. Technical Reviews. The Agency identified a change in the health
assessment that could lead to a change in the MCLG (USEPA, 2002i). EPA
updated the risk assessment in 1998. This new risk assessment
considered relevant studies that had become available on the toxicity
of picloram including its potential developmental and reproductive
toxicity. The new risk assessment revised the RfD from 0.07 mg/kg/day
to 0.20 mg/kg/day and classified picloram as Group E, evidence of
noncarcinogenicity for humans, according to the 1986 Cancer Guidelines.
Picloram has not been evaluated against the Proposed 1996 Cancer
Guidelines.
Based on the change in the RfD for picloram and using a 20 percent
RSC,\14\ EPA believes that any revision to the MCLG is not likely to be
higher than 1 mg/L (an increase in the MCLG).
---------------------------------------------------------------------------
\14\ This is the RSC used for the current MCLG and also the
default value. EPA has no reason to believe that the RSC for
picloram would change. See Appendix A for further discussion of the
RSC.
---------------------------------------------------------------------------
Analytical or treatment feasibility do not pose any limitations for
the current MCL and would not be a limiting factor if EPA were to raise
the MCLG. The Agency's review of possible ``other regulatory
revisions'' did not identify any issues that are specific to picloram
(USEPA, 2002e).
EPA evaluated the results of the occurrence and exposure analyses
for picloram to determine whether possible changes to the MCL would be
likely to result in opportunities for significant cost savings to PWSs
and their customers (USEPA, 2002g; USEPA, 2002h). Table V-13 shows the
results of the detailed occurrence and exposure analysis based on the
16-State cross-section for the current MCL (0.5 mg/L), and the
concentration that would be considered if the EPA revised the MCLG and
MCL (i.e., the possible MCLG/MCL of 1 mg/L) based on the new RfD and a
20 percent RSC. Based on the detailed analysis, it appears that
picloram is unlikely to occur at concentrations above 0.5 mg/L in the
States used for the cross-section.
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[[Page 19080]]
The results of the detailed occurrence and exposure analysis
indicate that few, if any, of the 12,907 systems sampled in the 16
cross-section States might be affected if EPA were to raise the MCLG/
MCL.
c. Preliminary Decision. Although there are new data that support
consideration of whether to revise the MCLG/MCL for picloram, EPA does
not believe a revision to the NPDWR for picloram is appropriate at this
time. The Agency believes that any change in the MCLG/MCL would be
unlikely to provide an opportunity for significant cost savings to
PWSs.
53. Polychlorinated Biphenyls (PCBs)
a. Background. EPA published the current NPDWR for PCBs on January
30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an MCLG of
zero based on a cancer classification of B2, probable human carcinogen.
The NPDWR also established an MCL of 0.0005 mg/L based on analytical
feasibility.
b. Technical Reviews. The Agency has initiated a reassessment of
the health risks resulting from exposure to PCBs. The revised risk
assessment will consider relevant studies that have become available on
the toxicity of PCBs including their potential developmental and
reproductive toxicity. The Agency expects the new risk assessment to be
completed in the 2002 or 2003 time frame (USEPA, 2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for PCBs is appropriate at this time because a reassessment
of the health risks resulting from exposure to PCBs is ongoing.
54. Selenium
a. Background. EPA published the current NPDWR for selenium on
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an
MCLG and an MCL of 0.05 mg/L. The Agency based the MCLG on an RfD of
0.005 mg/kg/day and a cancer classification of D, not classifiable as
to human carcinogenicity.
b. Technical Reviews. The Agency has not updated the risk
assessment for selenium since the NPDWR was published (USEPA, 2002i).
However, a 2000 NAS assessment of selenium supports the current RfD
based on epidemiological studies of selenosis in humans (NAS, 2000b).
The NAS study considered relevant studies that were available on the
toxicity of selenium, including its developmental and reproductive
toxicity, and established a tolerable upper intake level of 0.4 mg/day
for adolescents and adults, a value which is equivalent to the RfD.
A review of analytical or treatment feasibility is not necessary
for selenium because changes to the MCLG are not warranted at this
time, and the current MCL is set at the MCLG. In addition, the results
of EPA's review of possible ``other regulatory revisions'' did not
identify any selenium-specific issues (USEPA, 2002e). Since EPA did not
identify a health or technology basis for revising the selenium NPDWR,
the Agency did not conduct a detailed occurrence and exposure analysis.
c. Preliminary Decision. After reviewing the results of the
pertinent technical analyses, the Agency believes the NPDWR for
selenium remains appropriate and thus, it is not subject to revision at
this time.
55. Simazine
a. Background. EPA published the current NPDWR for simazine on July
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG and
an MCL of 0.004 mg/L. The Agency based the MCLG on an RfD of 0.005 mg/
kg/day and a cancer classification of C, possible human carcinogen.
b. Technical Reviews. The Agency has initiated a reassessment of
the health risks resulting from exposure to simazine. The revised risk
assessment will consider relevant studies that have become available on
the toxicity of simazine including its potential developmental and
reproductive toxicity. The Agency expects the new risk assessment to be
completed in the 2003 or 2004 time frame (USEPA, 2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for simazine is appropriate at this time because a
reassessment of the health risks resulting from exposure to simazine is
ongoing. The Agency is also re-examining all the triazines and their
degradation products as part of its CCL in order to fill any necessary
research gaps to enable the Agency to determine whether or not to
regulate any or all of the contaminants in this group of compounds.
56. Styrene
a. Background. EPA published the current NPDWR for styrene on
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an
MCLG and an MCL of 0.1 mg/L. The Agency based the MCLG on an RfD of 0.2
mg/kg/day and a cancer classification of C, possible human carcinogen.
b. Technical Reviews. The Agency has initiated a reassessment of
the health risks resulting from exposure to styrene. The revised risk
assessment will consider relevant studies that have become available on
the toxicity of styrene including its potential developmental and
reproductive toxicity. The Agency expects the new risk assessment to be
completed in the 2002 or 2003 time frame (USEPA, 2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for styrene is appropriate at this time because a
reassessment of the health risks resulting from exposure to styrene is
ongoing.
57. 2,3,7,8-TCDD (Dioxin)
a. Background. EPA published the current NPDWR for dioxin on July
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG of
zero based on a cancer classification of B2, probable human carcinogen.
The NPDWR also established an MCL of 3 x 10-8 mg/L based on
analytical feasibility.
b. Technical Reviews. The Agency has conducted a comprehensive
assessment of the exposure and potential human health effects of dioxin
including its potential developmental and reproductive toxicity. The
draft document has been reviewed by the SAB (USEPA, 2001b). The Agency
is presently in the process of addressing SAB and public comments, and
expects to complete the risk assessment in the 2002 or 2003 time frame.
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for dioxin is appropriate at this time because a reassessment
of the health risks resulting from exposure to dioxin is ongoing.
58. Tetrachloroethylene
a. Background. EPA published the current NPDWR for
tetrachloroethylene on January 30, 1991 (56 FR 3526 (USEPA, 1991a)).
The NPDWR established an MCLG of zero based on a cancer classification
of B2, probable human carcinogen. The NPDWR also established an MCL of
0.005 mg/L based on analytical feasibility.
b. Technical Reviews. EPA has initiated a reassessment of the
health risks resulting from exposure to tetrachloroethylene. The
revised risk assessment will consider relevant studies that have become
available on the toxicity of tetrachloroethylene including its
potential developmental and reproductive toxicity. The Agency expects
the new risk assessment to be completed in the 2002 or 2003 time frame
(USEPA, 2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for tetrachloroethylene is appropriate at this time because a
[[Page 19081]]
reassessment of the health risks resulting from exposure to
tetrachloroethylene is ongoing.
59. Thallium
a. Background. EPA published the current NPDWR for thallium on July
17, 1992 (57 FR 3526 (USEPA, 1991a)). The NPDWR established an MCLG of
0.0005 mg/L based on an RfD of 0.00007 mg/kg/day and a cancer
classification of D, not classifiable as to human carcinogenicity. The
NPDWR also established an MCL of 0.002 mg/L based on analytical
feasibility.
b. Technical Reviews. The results of the health effects technical
review identified some information on reproductive effects that
indicate the need to update the Agency's risk assessment for thallium
(USEPA, 2002i). In light of this information, EPA has initiated a
reassessment of the health risks resulting from exposure to thallium
and has already solicited scientific information from the public for
consideration (67 FR 1212, January 9, 2002 (USEPA, 2002a)). The new
risk assessment will consider relevant data on the toxicity of thallium
including its potential developmental and reproductive toxicity.
Because the new assessment is not expected to be completed until the
2004 or 2005 time frame, EPA does not believe it is appropriate to
revise the MCLG at this time.
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for thallium is appropriate at this time. A reassessment of
the health risks has been initiated and the Agency does not believe it
is appropriate to revise the NPDWR while that effort is in process.
60. Toluene
a. Background. EPA published the current NPDWR for toluene on
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an
MCLG and an MCL of 1 mg/L. The Agency based the MCLG on an RfD of 0.2
mg/kg/day and a cancer classification of D, not classifiable as to
human carcinogenicity.
b. Technical Reviews. The Agency has initiated a reassessment of
the health risks resulting from exposure to toluene. The revised risk
assessment will consider relevant studies that have become available on
the toxicity of toluene including its potential developmental and
reproductive toxicity. The Agency expects the new risk assessment to be
completed in the 2002 or 2003 time frame (USEPA, 2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for toluene is appropriate at this time because a
reassessment of the health risks resulting from exposure to toluene is
ongoing.
61. Toxaphene
a. Background. EPA published the current NPDWR for toxaphene on
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an
MCLG of zero based on a cancer classification of B2, probable human
carcinogen. The NPDWR also established an MCL of 0.003 mg/L based on
analytical feasibility.
b. Technical Reviews. The Agency has not updated the health risk
assessment for toxaphene since the NPDWR was published; however, ATSDR
completed a toxicological profile for toxaphene in 1996 (ATSDR, 1996d).
This assessment and other recent information do not warrant a review of
the cancer classification because the data indicate that toxaphene is
mutagenic and would be evaluated using a linear dose-response approach
(USEPA, 2002i). Accordingly, the MCLG remains at zero and the Agency
believes that a further review of the health effects of toxaphene is
not warranted at this time.
The current MCL for toxaphene is based on a PQL of 0.003 mg/L. As a
part of the Six-Year Review, EPA analyzed more recent WS data to
determine if it might be possible to recalculate the PQL (USEPA,
2002d). In addition, the Agency evaluated whether more sensitive
analytical methods have been approved and put into use by a wide number
of laboratories. The results of these analyses indicate that some
improvement in analytical feasibility might exist. Evaluation of the WS
data shows that EPA Regional and State laboratories exhibit greater
than 90 percent laboratory passing rates at concentrations around the
current PQL of 0.003 mg/L. Because most of the laboratory passing rates
exceeded the 75 percent criterion typically used to derive a PQL from
WS studies, this information indicates that a lower PQL corresponding
to the 75 percent passing rate might exist for toxaphene. While this
information is indicative of a possibly lower PQL, the WS data are
insufficient at this time to actually recalculate what the lower PQL
for toxaphene might be.
Using information about the analytical methods most widely used to
report results in the WS studies, the MDLs for these methods, and the
10 times MDL multiplier, EPA estimated what the possibly lower PQL/MCL
might be. For the analysis of toxaphene in the more recent WS studies,
laboratories predominantly used EPA Methods 508 (GC/MS) and 505 (Purge
and Trap GC). No MDL data are available for EPA Method 508 and the MDL
for 505 is listed as 0.001 mg/L. A 10 times MDL multiplier based on EPA
Method 505 predicts a PQL of 0.01 mg/L, which is higher than the
current PQL. Therefore, the 10 times multiplier could not be used to
predict a lower PQL and EPA did not use this higher value as a
threshold in the occurrence analysis discussed in this section.
Instead, EPA used concentration thresholds of one-half the current MCL
and the lower limit of detection reported by the States. EPA believes
if a lower PQL does exist, that the magnitude of the change would be
minimal.
Since the analytical feasibility analysis indicates that the PQL
for toxaphene (and therefore the MCL) could possibly be lower if EPA
had more definitive data to recalculate the PQL, EPA considered whether
treatment feasibility is likely to pose any limitations (USEPA, 2002k).
The current BAT for toxaphene is GAC. Compliance technologies for small
systems include GAC, PAC, and POU GAC. EPA believes that the BAT and
compliance technologies are still practical and would not pose any
limitations for toxaphene at a possibly lower MCL.
The results of EPA's review of possible ``other regulatory
revisions'' did not identify any issues that are specific to toxaphene
(USEPA, 2002e).
EPA evaluated the results of the occurrence and exposure analyses
for toxaphene to determine whether changes to the MCL might be
appropriate and likely to result in additional public health protection
if EPA had sufficient data to recalculate the PQL (USEPA, 2002g; USEPA,
2002h). Table V-14 shows the results of the detailed occurrence and
exposure analyses based on the 16-State cross-section for the current
MCL (0.003 mg/L), one-half the current MCL (0.0015 mg/L), and the lower
level of detection reported by the States (0.001 mg/L).
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The detailed occurrence and exposure analysis indicates that
toxaphene is unlikely to occur at the current MCL or any potential MCL
revision for the States used in the cross-section. Since toxaphene uses
were canceled in the United States in 1990 and since it is subject to
the United Nations Prior Informed Consent (USEPA, 2002g; USEPA, 2002h),
EPA expects the occurrence of toxaphene in PWSs to be rare.
c. Preliminary Decision. Although there are new data that support
consideration of a possibly lower PQL (and therefore a possibly lower
MCL), EPA does not believe a revision to the NPDWR for toxaphene is
appropriate at this time. The Agency does not have sufficient data at
this time on which to base a PQL recalculation and hence an MCL
revision. Also, the Agency believes that any change in the PQL would be
minimal and unlikely to significantly improve the level of public
health protection because toxaphene appears to occur infrequently at
concentrations at or below the current MCL.
62. 2,4,5-TP (Silvex; 2,4,5-Trichlorophenoxypropionic Acid)
a. Background. EPA published the current NPDWR for 2,4,5-TP on
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an
MCLG and an MCL of 0.05 mg/L. The Agency based the MCLG on an RfD of
0.008 mg/kg/day and a cancer classification of D, not classifiable as
to human carcinogenicity.
b. Technical Reviews. The Agency has not updated the health risk
assessment for 2,4,5-TP since the NPDWR was published. Therefore, as
part of the Six-Year Review process, EPA conducted a literature search
for relevant data on the toxicology of 2,4,5-TP including its potential
developmental and reproductive toxicity. The literature search did not
identify any new studies that warrant a review of the RfD or the cancer
classification (USEPA, 2002i).
A review of analytical or treatment feasibility is not necessary
for 2,4,5-TP because changes to the MCLG are not warranted at this time
and the current MCL is set at the MCLG. In addition, the
[[Page 19083]]
results of EPA's review of possible ``other regulatory revisions'' did
not identify any 2,4,5-TP-specific issues (USEPA, 2002e). Since EPA did
not identify a health or technology basis for revising the 2,4,5-TP
NPDWR, the Agency did not conduct a detailed occurrence and exposure
analysis.
c. Preliminary Decision. After reviewing the results of the
pertinent technical analyses, the Agency believes the NPDWR for 2,4,5-
TP remains appropriate and thus, it is not subject to revision at this
time.
63. 1,2,4-Trichlorobenzene
a. Background. EPA published the current NPDWR for 1,2,4-
trichlorobenzene on July 17, 1992 (57 FR 31776 (USEPA, 1992)). The
NPDWR established an MCLG and an MCL of 0.07 mg/L. The Agency based the
MCLG on an RfD of 0.01 mg/kg/day and a cancer classification of D, not
classifiable as to human carcinogenicity.
b. Technical Reviews. The Agency has not updated the health risk
assessment for 1,2,4-trichlorobenzene since the NPDWR was published.
Therefore, as part of the Six-Year Review process, EPA conducted a
literature search for relevant data on the toxicology of 1,2,4-
trichlorobenzene, including its potential developmental and
reproductive toxicity. The literature search did not identify any new
studies that warrant a review of the RfD or the cancer classification
(USEPA, 2002i).
A review of analytical or treatment feasibility is not necessary
for 1,2,4-trichlorobenzene because changes to the MCLG are not
warranted at this time and the current MCL is set at the MCLG. In
addition, the results of EPA's review of possible ``other regulatory
revisions'' did not identify any 1,2,4-trichlorobenzene-specific issues
(USEPA, 2002e). Since EPA did not identify a health or technology basis
for revising the 1,2,4-trichlorobenzene NPDWR, the Agency did not
conduct a detailed occurrence and exposure analysis.
c. Preliminary Decision. After reviewing the results of the
pertinent technical analyses, the Agency believes the NPDWR for 1,2,4-
trichlorobenzene remains appropriate and thus, it is not subject to
revision at this time.
64. 1,1,1-Trichloroethane
a. Background. EPA published the current NPDWR for 1,1,1-
trichloroethane on July 8, 1987 (52 FR 25690 (USEPA, 1987)). The NPDWR
established an MCLG and an MCL of 0.20 mg/L. The Agency developed the
MCLG based on an RfD of 0.035 mg/kg/day derived from an inhalation
study and a cancer classification of D, not classifiable as to human
carcinogenicity.
b. Technical Reviews. The Agency has initiated a reassessment of
the health risks resulting from exposure to 1,1,1-trichloroethane. The
revised risk assessment will consider relevant studies that have become
available on the toxicity of toluene including its potential
developmental and reproductive toxicity. The Agency expects the new
risk assessment to be completed in the 2003 or 2004 time frame (USEPA,
2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for 1,1,1-trichloroethane is appropriate at this time because
a reassessment of the health risks resulting from exposure to 1,1,1-
trichloroethane is ongoing.
65. 1,1,2-Trichloroethane
a. Background. EPA published the current NPDWR for 1,1,2-
trichloroethane on July 17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR
established an MCLG of 0.003 mg/L based on an RfD of 0.004 mg/kg/day
and a cancer classification of C, possible human carcinogen. The NPDWR
also established an MCL of 0.005 mg/L based on analytical feasibility.
b. Technical Reviews. The Agency has not updated the health risk
assessment for 1,1,2-trichloroethane since the NPDWR was published.
Therefore, as part of the Six-Year Review process, EPA conducted a
literature search for relevant data on the toxicology of 1,1,2-
trichloroethane including its potential developmental and reproductive
toxicity. The literature search did not identify any studies that
warrant a review of the RfD or the cancer classification (USEPA,
2002i).
The current MCL for 1,1,2-trichloroethane is based on a PQL of
0.005 mg/L. As a part of the Six-Year Review, EPA analyzed more recent
WS data to determine if it might be possible to recalculate the PQL
(USEPA, 2002d). In addition, the Agency evaluated whether more
sensitive analytical methods have been approved and put into use by a
wide number of laboratories. The results of these analyses indicate
that a slight improvement in analytical feasibility might exist.
Evaluation of the WS data shows that EPA Regional and State
laboratories exhibit greater than 90 percent laboratory passing rates
at concentrations around the current PQL of 0.005 mg/L. Because most of
the laboratory passing rates exceeded the 75 percent criterion
typically used to derive a PQL from WS studies, this information
indicates that a lower PQL corresponding to the 75 percent passing rate
might exist for 1,1,2-trichloroethane. While this information is
indicative of a possibly lower PQL, the WS data are insufficient at
this time to actually recalculate what the lower PQL for 1,1,2-
trichloroethane might be.
Using information about the analytical methods most widely used to
report results in the WS studies, the MDLs for these methods, and the
10 times MDL multiplier, EPA estimated what the possibly lower PQL/MCL
might be. For the analysis of 1,1,2-trichloroethane in the more recent
WS studies, laboratories predominantly used EPA Methods 524.2 (GC/MS)
and 502.2 (Purge and Trap GC), which both have upper limit MDLs of
0.00003 mg/L. A 10 times MDL multiplier predicts a PQL of 0.0003 mg/L.
Since this value is below the current MCLG, this supports consideration
of whether the MCL might be set at the MCLG if sufficient data were
available to recalculate the PQL. EPA did not use the possibly lower
PQL as a threshold in the occurrence analysis but instead used 0.003
mg/L (the current MCLG) since this is the lowest level to which the MCL
would possibly be revised.
Since the analytical feasibility analysis indicates that the PQL
for 1,1,2-trichloroethane (and therefore the MCL) could possibly be
lower if EPA had more definitive data to recalculate the PQL, EPA
considered whether treatment feasibility is likely to pose any
limitations (USEPA, 2002k). The current BATs for 1,1,2-trichloroethane
include both PTA and GAC. Small system compliance technologies for
1,1,2-trichloroethane include GAC and several aeration technologies.
EPA believes that these BATs and compliance technologies are still
practical and would not pose any limitations for 1,1,2-trichloroethane
at a possibly lower level.
The results of EPA's review of possible ``other regulatory
revisions'' did not identify any issues that are specific to 1,1,2-
trichloroethane (USEPA, 2002e).
EPA evaluated the results of the occurrence and exposure analyses
for 1,1,2-trichloroethane to determine whether changes to the MCL might
be appropriate and likely to result in additional public health
protection if sufficient data were available to recalculate the PQL and
subsequently set the MCL at the MCLG (USEPA, 2002g; USEPA, 2002h).
Table V-15 shows the results of the detailed occurrence and exposure
analyses based on the 16-State cross-section for the current MCL (0.005
mg/L) and the potentially revised MCL (0.003 mg/L)
[[Page 19084]]
based on setting the MCL at the MCLG. Based on the detailed analysis,
it appears that 1,1,2-trichloroethane is unlikely to occur at the
current MCL or any potential MCL revisions in the States used for the
cross-section.
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c. Preliminary Decision. Although there are new data that support
consideration of whether a lower PQL is possible (and therefore a
possibly set the MCL at the MCLG), EPA does not believe a revision to
the NPDWR for 1,1,2-trichloroethane is appropriate at this time. The
Agency believes that any potential revision to the MCL is unlikely to
significantly improve the level of public health protection because
1,1,2-trichloroethane appears to occur infrequently at concentrations
at or below the current MCL.
66. Trichloroethylene
a. Background. EPA published the current NPDWR for
trichloroethylene on July 8, 1987 (52 FR 25690 (USEPA, 1987)). The
NPDWR established an MCLG of zero based on a cancer classification of
B2, probable human carcinogen. The NPDWR also established an MCL of
0.005 mg/L based on analytical feasibility.
b. Technical Reviews. EPA has initiated a reassessment of the
health risks resulting from exposure to trichloroethylene. The revised
risk assessment will consider relevant studies that have become
available on the toxicity of trichloroethylene including its potential
developmental and reproductive toxicity. The Agency expects the new
risk assessment to be completed in the 2002 or 2003 time frame (USEPA,
2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for trichloroethylene is appropriate at this time because a
reassessment of the health risks resulting from exposure to
trichloroethylene is ongoing.
67. Vinyl Chloride
a. Background. EPA published the current NPDWR for vinyl chloride
on July 8, 1987 (52 FR 25690 (USEPA, 1987)). The NPDWR established an
MCLG of zero based on a cancer classification of A, known human
carcinogen. The NPDWR also established an MCL of 0.002 mg/L based on
analytical feasibility.
b. Technical Reviews. The Agency updated the health risk assessment
of vinyl chloride in 2000 (USEPA, 2000k). The updated risk assessment
included relevant studies that were available on the toxicity of vinyl
chloride including its potential developmental and reproductive
toxicity. According to the 1986 EPA Guidelines for Carcinogen Risk
Assessment, vinyl chloride is categorized as Group A, known human
carcinogen. Under the Proposed Guidelines for Carcinogen Risk
Assessment (61 FR 17960, April 23, 1996 (USEPA, 1996)), EPA concluded
that vinyl chloride is a known human carcinogen by the inhalation route
of exposure, based on human epidemiological data and, by analogy, by
the oral and dermal routes.
The current MCL for vinyl chloride is based on a PQL of 0.002 mg/L.
As a part
[[Page 19085]]
of the Six-Year Review, EPA analyzed WS data to determine if it might
be possible to recalculate the PQL. In addition, the Agency evaluated
whether more sensitive analytical methods have been approved and put
into use by a wide number of laboratories. Based on these analyses, the
Agency believes the current PQL, and therefore the MCL, is still
appropriate (USEPA, 2002d).
A review of treatment feasibility is not necessary for vinyl
chloride because no changes to the MCLG or the MCL are warranted at
this time. In addition, the results of EPA's review of possible ``other
regulatory revisions'' did not identify any vinyl chloride-specific
issues (USEPA, 2002e). Since EPA did not identify a health or
technology basis for revising the vinyl chloride NPDWR, the Agency did
not conduct a detailed occurrence and exposure analysis.
c. Preliminary Decision. After reviewing the results of the
pertinent technical analyses, the Agency believes the NPDWR for vinyl
chloride remains appropriate and thus, it is not subject to revision at
this time.
68. Xylenes (Total)
a. Background. EPA published the current NPDWR for total xylenes on
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an
MCLG and an MCL of 10 mg/L. The Agency based the MCLG on an RfD of 2
mg/kg/day and a cancer classification of D, not classifiable as to
human carcinogenicity.
b. Technical Reviews. The Agency has initiated a reassessment of
the health risks resulting from exposure to xylenes. The revised risk
assessment will consider relevant studies that have become available on
the toxicity of xylenes including its potential developmental and
reproductive toxicity. The Agency expects the new risk assessment to be
completed in the 2002 or 2003 time frame (USEPA, 2002i).
c. Preliminary Decision. The Agency does not believe a revision to
the NPDWR for xylenes is appropriate at this time because a
reassessment of the health risks resulting from exposure to xylenes is
ongoing.
B. What Preliminary Decision Has EPA Made Regarding the Total Coliform
Rule?
1. Background
EPA published the TCR on June 29, 1989 (54 FR 27544 (USEPA,
1989b)). The TCR is one of several EPA regulations that protect the
public from pathogens in drinking water. The TCR requires all PWSs to
monitor for the presence of total coliforms in the distribution system.
Total coliforms are a group of closely related bacteria that are (with
few exceptions) not harmful to humans. They are natural and common
inhabitants of the soil and ambient waters (e.g., lakes, rivers and
estuaries), as well as in the gastrointestinal tract of animals. A few
of these coliforms (fecal coliforms, including Escherichia coli or E.
coli \15\) only grow within the intestinal tract of humans and other
warm-blooded animals. Total coliforms may be injured by environmental
stresses (e.g., lack of nutrients) and water treatment (e.g., chlorine
disinfection) in a manner similar to most bacterial pathogens and many
virus pathogens. Therefore, EPA considers them a useful indicator of
bacterial and many viral waterborne enteric pathogens. More
specifically, for drinking water, total coliforms are used to determine
the adequacy of water treatment and the integrity of the distribution
system. The absence of total coliforms in the distribution system
minimizes the likelihood that fecal pathogens are present. Thus, total
coliforms are used to determine the vulnerability of a system to fecal
contamination.
---------------------------------------------------------------------------
\15\ EPA is aware that Escherichia coli O157 may be found in
fecally contaminated drinking water. To date, however, none of the
EPA-approved methods for E. coli and fecal coliforms in drinking
water detect E. coli O157. Nevertheless, E. coli O157, as is true
with nonpathogenic E. coli strains, is always associated with fecal
waste (outside the laboratory) and should be as susceptible to
disinfection as the nonpathogenic strains. Therefore, the presence
of E. coli O157 should always be accompanied by other E. coli
strains that are detectable by the EPA-approved methods.
---------------------------------------------------------------------------
The 1989 TCR set an MCLG of zero for total coliforms because EPA
was not aware of any data in the scientific literature supporting a
particular value for the concentration of coliforms below which no
known or anticipated adverse health effects occur, with an adequate
margin of safety. The TCR requires systems to monitor for total
coliforms at a frequency proportional to the number of people served.
If any sample is total coliform-positive, the system must:
Test the positive culture for the presence of either fecal
coliforms or E. coli;
Take one set of 3-4 repeat samples at sites located within
five or fewer sampling sites adjacent to the location of the routine
positive sample within 24 hours; and
Take at least 5 routine samples the next month of
operation.
2. Technical Reviews
Since the TCR was promulgated in 1989, few technical papers on the
occurrence of coliforms in treated water have been published. Much of
the recent technical data on coliforms are associated with biofilm
studies, specifically the factors that facilitate the growth of
coliforms and other microbes within the distribution system (e.g.,
LeChevallier et al., 1991, 1996; LeChevallier, 1999). In addition,
several studies have been published describing the performance of new
coliform methods (e.g., Brenner et al., 1993; Grant, 1997).
One recent study examined the relationship between total coliforms
and waterborne disease outbreaks (Craun et al., 1997). According to the
study results, coliforms were found in 84 percent of the 187 systems
during an outbreak investigation, but in the months before any
outbreak, they were only detected by 26 percent of these systems. For
outbreaks caused by Cryptosporidium or Giardia, coliforms were only
found during 38 percent of the outbreaks. The study, as well as data
from the 1993 outbreak of waterborne cryptosporidiosis in Milwaukee
(MacKenzie, et al., 1994), continues to support the premise that
coliforms are an inadequate indicator for Cryptosporidium oocysts and
Giardia cysts in treated waters, presumably because these protozoa are
appreciably more resistant to disinfection than the coliform
indicators.
Since promulgation of the TCR, EPA has received comments from a
number of stakeholders. Stakeholders have suggested modifications to
reduce the burden of implementing the TCR. EPA has determined that an
opportunity for implementation burden reduction exists and will analyze
the effect that such changes would have on public health protection as
part of the Agency's regulatory development/revision process. Only
those measures which reduce the TCR implementation burden while still
assuring public health protection will be considered by EPA.
3. Preliminary Decision
EPA intends to undertake a rulemaking process to initiate possible
revisions to the TCR. As part of this process, EPA believes it may be
appropriate to include this rulemaking in a wider effort to review and
address broader issues associated with drinking water distribution
systems. This would be one way of addressing some of the
recommendations of the Microbial/ Disinfection Byproducts (M/DBP)
Federal Advisory Committee in the Stage 2 M/DBP Agreement in Principle
(65 FR 83015, December 29, 2000 (USEPA, 2000h)). As part of the TCR
rulemaking, EPA plans to assess the
[[Page 19086]]
effectiveness of the current TCR in reducing public health risk, and
what technically supportable alternative/additional monitoring
strategies are available that would decrease economic burden while
maintaining or improving public health protection.
VI. Request for Comments
A. On Which Issues Is EPA Soliciting Public Comment?
Today's action solicits public comment on the following broad
issues.
(1) Is EPA's protocol for the review of the 69 NPDWRs discussed in
today's action reasonable and appropriate?
(2) Based on the review, are EPA's revise/not revise conclusions
appropriate for each of the 69 NPDWRs?
EPA also invites commenters to submit any new, relevant peer-
reviewed data pertaining to the NPDWRs discussed in today's action.
Peer-reviewed data are studies/analyses that have been reviewed by
qualified individuals (or organizations) who are independent of those
who performed the work, but who are collectively equivalent in
technical expertise (i.e., peers) to those who performed the original
work. A peer review is an in-depth assessment of the assumptions,
calculations, extrapolations, alternate interpretations, methodology,
acceptance criteria, and conclusions pertaining to the specific major
scientific and/or technical work products and of the documentation that
supports them (USEPA, 2000i). Relevant data include studies/analyses
pertaining to health effects, analytical feasibility, treatment
feasibility, and occurrence/exposure related to the contaminants
discussed in today's action.
Table VI-1 summarizes the specific comments requested in today's
action and provides a cross reference to the section of today's action
where the issue is discussed.
BILLING CODE 6560-50-P
[GRAPHIC] [TIFF OMITTED] TP17AP02.025
BILLING CODE 6560-50-C
EPA also invites commenters to submit any new, relevant peer-
reviewed data pertaining to the NPDWRs discussed in today's action.
B. Request for Comments on Use of Plain Language
Executive Order 12866 and the President's memorandum of June 1,
1998, require each agency to write all rules in plain language. We
invite your comments on how to make this action easier to understand.
For example:
Have we organized the material to suit your needs?
Are the decisions in the notice and our rationale for
those decisions clearly stated?
Does the notice contain technical language or jargon that
isn't clear?
Would a different format (grouping and order of sections,
use of headings, paragraphing) make the notice easier to understand?
Would more (but shorter) sections be better?
Could we improve clarity by adding tables, lists, or
diagrams?
What else could we do to make the notice easier to
understand?
VII. EPA's Next Steps
EPA plans a 60-day comment period following this action. For each
NPDWR for which the Agency has published its preliminary revise/not
revise decision in today's action, EPA will consider the public
comments received and review any new peer-reviewed data submitted in
support of those public comments to determine whether a different
revise/not revise decision is appropriate in light of the submitted
data. The Agency plans to publish its final revise/not revise decisions
for these NPDWRs in the August 2002 time frame.
The publication of a decision to revise pursuant to SDWA Section
1412(b)(9) is not the end of the regulatory process, but is the
beginning of one. A decision to revise starts a regulatory process for
a contaminant that involves more detailed analyses concerning health
effects, costs, benefits, occurrence, and other matters relevant to
deciding whether and how an NPDWR should be revised. At any point in
this process, EPA may find that regulatory revisions are no longer
appropriate and may discontinue regulatory revision efforts at that
time. Review of that contaminant would continue in future six-year
reviews.
Similarly, a decision not to revise at this time means only that
EPA does not believe that regulatory changes to a particular NPDWR are
appropriate now, based on lack of new data, ongoing scientific reviews,
low priority, or other reasons discussed in this action. Review of
these contaminants continues and future six-year reviews may lead to a
decision that regulatory changes are appropriate.
VIII. References
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ATSDR. 1993. Toxicological Profile for Heptachlor and Heptachlor
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ATSDR. 1996a. Toxicological Profile for 1,2-Dichloroethene. U.S.
Department of Health and Human Services, Public
[[Page 19087]]
Health Service. 196 pp. Available on the Internet at: http://www.atsdr.cdc.gov/toxprofiles/tp87.html.
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ATSDR. 1996c. Toxicological Profile for Hexachlorobenzene. U.S.
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and J.P. Davis. 1994. A massive outbreak in Milwaukee of
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NAS. 2000b. Dietary reference intakes for vitamin C, vitamin E,
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http://www.epa.gov/safewater/ndwac/guidfnl.pdf.
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USEPA. 1975. Water Programs: National Interim Primary Drinking Water
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24, 1975.
USEPA. 1976. Interim Primary Drinking Water Regulations;
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USEPA. 1979. National Interim Primary Drinking Water Regulations;
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44, No. 231. p. 68624, November 29, 1979.
USEPA. 1985. National Primary Drinking Water Regulations; Volatile
Synthetic Organic Chemicals; Final Rule and Proposed Rule. Federal
Register. Vol. 50, No. 219. p. 46880, November 13, 1985.
USEPA. 1986a. National Primary and Secondary Drinking Water
Regulations; Fluoride; Final Rule. Federal Register. Vol. 51, No.
63. p. 11396, April 2, 1986.
USEPA. 1986b. EPA Guidelines for Carcinogen Risk Assessment. Federal
Register. Vol. 51, No. 185. p. 33992, September 24, 1986.
USEPA. 1987. National Primary Drinking Water Regulations--Synthetic
Organic Chemicals; Monitoring for Unregulated Contaminants; Final
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USEPA. 1989a. National Primary and Secondary Drinking Water
Regulations; Proposed Rule. Federal Register. Vol. 54, No. 97. p.
22062, May 22, 1989.
USEPA. 1989b. Drinking Water; National Primary Drinking Water
Regulations; Total Coliforms (Including Fecal Coliforms and E.
coli); Final Rule. Federal Register. Vol. 54, No. 124. p. 27544,
June 29, 1989.
USEPA. 1989c. National Primary Drinking Water Regulations;
Filtration, Disinfection; Turbidity, Giardia Lamblia, Viruses,
Legionella, and Heterotrophic Bacteria; Final Rule. Part 2. Federal
Register. Vol. 54, No. 124. p. 27486, June 29, 1989.
USEPA. 1990. National Primary and Secondary Drinking Water
Regulations--Synthetic Organic Chemicals and Inorganic Chemicals;
Proposed Rule. Federal Register. Vol. 55, No. 143. p. 30370, July
25, 1990.
USEPA. 1991a. National Primary Drinking Water Regulations--Synthetic
Organic Chemicals and Inorganic Chemicals; Monitoring for
Unregulated Contaminants; National Primary Drinking Water
Regulations Implementation; National Secondary Drinking Water
Regulations; Final Rule. Federal Register. Vol. 56, No. 30. p. 3526,
January 30, 1991.
USEPA. 1991b. Drinking Water Regulations--Maximum Contaminant Level
Goals and National Primary Drinking Water Regulations for Lead and
Copper; Final Rule. Federal Register. Vol. 56, No. 110. p. 26460,
June 7, 1991.
USEPA. 1991c. Drinking Water; National Primary Drinking Water
Regulations; Monitoring for Volatile Organic Chemicals; MCLGs and
MCLs for Aldicarb, Aldicarb Sulfoxide, Aldicarb Sulfone,
Pentachlorophenol, and Barium; Final Rule. Federal Register. Vol.
56, No. 126. p. 30266, July 1, 1991.
USEPA. 1992. Drinking Water; National Primary Drinking Water
Regulations--Synthetic Organic Chemicals and Inorganic Chemicals;
National Primary Drinking Water Regulations Implementation; Final
Rule. Federal Register. Vol. 57, No. 138. p. 31776, July 17, 1992.
USEPA. 1994a. Public Water System Warning: Cyanide. Memo from
William R. Diamond, Acting Director of Drinking Water Standards
Division, Office of Ground Water and Drinking Water. March 7, 1994.
USEPA. 1994b. Drinking Water; Maximum Contaminant Level Goals and
National Primary Drinking Water Regulations for
[[Page 19088]]
Lead and Copper; Final Rule; Technical Corrections. Federal
Register. Vol. 59, No. 125. p. 33860, June 30, 1994.
USEPA. 1995. Integrated Risk Information System (IRIS), Mercuric
Chloride. Available on the Internet at: http://www.epa.gov/iris/subst/0692.htm.
USEPA. 1996. Proposed guidelines for carcinogen risk assessment.
Federal Register. Vol. 61, No. 79. p. 17960, April 23, 1996.
USEPA. 1997a. Alternative Monitoring Guidelines. EPA Report 816-R-
97-011. August 1997. Available on the Internet at: http://www.epa.gov/safewater/regs/pmrfin.html.
USEPA. 1997b. Mercury Study Report to Congress; Volume V: Health
Effects of Mercury and Mercury Compounds. EPA Report 452-R-97-009.
Office of Air Quality Planning and Standards, Office of Research and
Development. December 1997. Available on the Internet at:
http://www.epa.gov/ttn/oarpg/t3/reports/volume5.pdf.
USEPA. 1998a. Small System Compliance Technology List for Non-
Microbial Contaminants Regulated Before 1996. EPA Report 815-R-98-
002. September 1998.
USEPA. 1998b. National Primary Drinking Water Regulations:
Disinfectants and Disinfection Byproducts; Final Rule. Federal
Register. Vol. 63, No. 241. p. 69389, December 16, 1998.
USEPA. 1998c. National Primary Drinking Water Regulations: Interim
Enhanced Surface Water Treatment; Final Rule. Federal Register. Vol.
63, No. 241. p. 69478, December 16, 1998.
USEPA. 1998d. IRIS, Beryllium and Compounds. Available on the
Internet at: http://www.epa.gov/iris/subst/0012.htm.
USEPA. 1998e. IRIS, Chlordane (Technical). Available on the Internet
at: http://www.epa.gov/iris/subst/0142.htm.
USEPA. 1998f. IRIS, Chromium (VI). Available on the Internet at:
http://www.epa.gov/iris/subst/0144.htm.
USEPA. 1999a. Response to Recommendations from the Children's Health
Protection Advisory Committee Regarding Evaluation of Existing
Environmental Standards; Notice. Federal Register. Vol. 64, No. 22.
p. 5277, February 3, 1999.
USEPA. 1999b. Guidelines for Carcinogen Risk Assessment. NCEA-F-0644
Review Draft. U.S. Environmental Protection Agency Risk Assessment
Forum. Washington, D.C. July 1999.
USEPA. 1999c. Announcement of Stakeholders Meeting on the Drinking
Water Contaminant Identification and Selection Process, and the 6-
Year Review of All Existing National Primary Drinking Water
Regulations, as Required by the Safe Drinking Water Act, as Amended
in 1996; Notice of Stakeholders Meeting. Federal Register. Vol. 64,
No. 198. p. 55711, October 14, 1999.
USEPA. 1999d. A Review of Contaminant Occurrence in Public Water
Systems. EPA Report 816-R-99-006. November 1999. Available on the
Internet at: http://www.epa.gov/safewater/occur/nov99_lo.pdf.
USEPA. 1999e. Stakeholder Meeting on the Contaminant Candidate List
and the 6-Year Review of Existing National Primary Drinking Water
Regulations. November 1999. Available on the Internet at: http://www.epa.gov/safewater/ccl/novmtg.html.
USEPA. 1999f. IRIS, Barium and Compounds. Available on the Internet
at: http://www.epa.gov/iris/subst/0010.htm.
USEPA. 2000a. National Primary Drinking Water Regulations for Lead
and Copper; Final Rule. Federal Register. Vol. 65, No. 8. p. 1950,
January 12, 2000.
USEPA. 2000b. Working Group Meeting on Contaminant Candidate List
Regulatory Determinations and the 6-Year Review of Existing
Regulations. Office of Water. June 2000. Available on the Internet
at: http://www.epa.gov/safewater/ccl/junemtg.html.
USEPA. 2000c. Working Group Meeting on Contaminant Candidate List
Regulatory Determinations and the 6-Year Review of Existing
Regulations. Office of Water. July 2000. Available on the Internet
at: http://www.epa.gov/safewater/ccl/julymtg.html.
USEPA. 2000d. NDWAC Working Group Meeting on Contaminant Candidate
List Regulatory Determinations and the 6-Year Review of Existing
Regulations. Office of Water. September 2000. Available on the
Internet at: http://www.epa.gov/safewater/ccl/25septmtg.html.
USEPA. 2000e. Interim Reregistration Eligibility Decision (IRED)--
Oxamyl. EPA Report 738-R-00-015. Office of Prevention, Pesticides,
and Toxic Substances. October 2000. Available on the Internet at:
http://www.epa.gov/oppsrrd1/REDs/0253ired.pdf.
USEPA. 2000f. Methodology for Deriving Ambient Water Quality
Criteria for the Protection of Human Health. EPA Report 882-B-00-
004. Office of Water. October 2000.
USEPA. 2000g. National Primary Drinking Water Regulations;
Radionuclides; Final Rule. Federal Register. Vol. 65, No. 236. p.
76707, December 7, 2000.
USEPA. 2000h. Stage 2 Microbial and Disinfection Byproducts Federal
Advisory Committee Agreement in Principle; Notice. Federal Register.
Vol. 65, No. 251. p. 83015, December 29, 2000.
USEPA. 2000i. Science Policy Council Handbook: Peer Review, 2nd
Edition. EPA Report 100-B-00-001. Office of Science Policy, Office
of Research and Development. December 2000.
USEPA. 2000j. IRIS, Benzene. Available on the Internet at: http://www.epa.gov/iris/subst/0276.htm.
USEPA. 2000k. IRIS, Vinyl Chloride. Available on the Internet at:
http://www.epa.gov/iris/subst/1001.htm.
USEPA. 2000l. EPA Summary Report. Characterization of data
variability and uncertainty: Health effects assessments in the
Integrated Risk Information System (IRIS). In response to Congress,
HR 106-379. EPA Report 635-R-00-005F. National Center for
Environmental Assessment, Office of Research and Development.
USEPA. 2001a. National Primary Drinking Water Regulation; Arsenic
and Clarifications to Compliance and New Source Contaminants
Monitoring; Final Rule. Federal Register. Vol. 66, No. 14. p. 6975,
January 22, 2001.
USEPA. 2001b. Dioxin Reassessment--An SAB Review of the Office of
Research and Development's Reassessment of Dioxin. EPA Report SAB-
EC-01-006. May 2001. Available on the Internet at: http://www.epa.gov/sab/ec01006.pdf.
USEPA. 2001c. IRIS, Hexachlorocyclopentadiene. Available on the
Internet at: http://www.epa.gov/iris/subst/0059.htm.
USEPA. 2002a. Integrated Risk Information System (IRIS);
Announcement of 2002 Program; Request for Information; Notice.
Federal Register. Vol. 67, No. 6. p. 1212, January 9, 2002.
USEPA. 2002b. National Primary Drinking Water Regulations: Long-Term
1 Enhanced Surface Water Treatment Rule; Final Rule. Federal
Register. Vol. 67, No. 9. p. 1811, January 14, 2002.
USEPA. 2002c. An Evaluation of Available Economic Information in
Support of the Six-Year Review of Existing National Primary Drinking
Water Regulations. Memo from Marc Parrotta, Targeting and Analysis
Branch, Office of Ground Water and Drinking Water. March 2002.
USEPA. 2002d. Analytical Feasibility Support Document for the Six-
Year Review of Existing National Primary Drinking Water Regulations
(Reassessment of Feasibility for Chemical Contaminants). EPA Report
815-D-02-002. Draft. March 2002.
USEPA. 2002e. Consideration of Other Regulatory Revisions for
Chemical Contaminants in Support of the Six-Year Review of National
Primary Drinking Water Regulations. EPA Report 815-D-02-003. Draft.
March 2002.
USEPA. 2002f. EPA Protocol for Review of Existing National Primary
Drinking Water Regulations. EPA Report 815-D-02-004. Draft. March
2002.
USEPA. 2002g. Occurrence Estimation Methodology and Occurrence
Findings Report for the Six-Year Regulatory Review. EPA Report 815-
D-02-005. Draft. March 2002.
USEPA. 2002h. Occurrence Summary and Use Support Document for the
Six-Year Regulatory Review. EPA Report 815-D-02-006. Draft. March
2002.
USEPA. 2002i. Six-Year Review--Chemical Contaminants--Health Effects
Technical Support Document. EPA Report 822-R-02-001. Draft. February
2002.
USEPA. 2002j. Six-Year Review of the Total Coliform Rule--Comments
Received. Memo from Kenneth H. Rotert, Standards and Risk Reduction
Branch, Office of Ground Water and Drinking Water. March 2002.
USEPA. 2002k. Water Treatment Technology Feasibility Support
Document for Chemical Contaminants; In Support of
[[Page 19089]]
EPA Six-Year Review of National Primary Drinking Water Regulations.
EPA Report EPA 815-D-02-001. Draft. February 2002.
Dated: March 28, 2002.
Christine Todd Whitman,
Administrator.
Appendix A: Background on the Calculation of MCLG and Cancer
Classification System
Since the identification of contaminants for potential revision
may be dependent on whether or not the maximum contaminant level
goal (MCLG) could change, a brief explanation of the derivation of
the MCLG is warranted. The MCLG is the maximum level of a
contaminant in drinking water at which no known or anticipated
adverse health effects occur, allowing for an adequate margin of
safety. MCLGs are non-enforceable health goals. EPA establishes the
maximum contaminant level (MCL) based on the MCLG. The MCL is the
maximum permissible level of a contaminant in water which is
delivered to any user of a public water system. It is derived based
on the MCLG. Prior to the 1996 Amendments to the Safe Drinking Water
Act (SDWA), the MCL was set as close to the MCLG as is feasible,
taking costs into consideration. The 1996 Amendments to the SDWA
permit consideration of costs relative to benefits in establishing a
MCL. MCLs are enforceable standards.
For chemicals exhibiting a threshold for toxic effects, EPA
establishes the MCLG on the basis of an oral reference dose (RfD). A
change in the RfD could lead to a change in the MCLG and thus in the
MCL. The RfD is an estimate (with uncertainty spanning perhaps an
order of magnitude) of a daily oral exposure to the human population
(including sensitive subgroups) that is likely to be without an
appreciable risk of deleterious noncancer effects during a lifetime.
The RfD is derived as follows:
[GRAPHIC] [TIFF OMITTED] TP17AP02.027
Where:
NOAEL = no-observed-adverse-effect level
LOAEL = lowest-observed-adverse-effect level
BMD = benchmark dose
UF = uncertainty factor
MF = modifying factor
The benchmark dose (BMD) is the statistical lower confidence limit
on the dose estimated to produce a predetermined level of change
(i.e., 10 percent) in the critical response relative to the control.
The uncertainty factor (UF) is used to account for extrapolation
uncertainties (e.g., inter-individual variation, interspecies
differences, duration of exposure, and use of a LOAEL instead of a
NOAEL) and database adequacy. The modifying factor (MF) is used as a
judgment factor to account for the confidence in the critical study
(or studies) used in the derivation of the RfD (USEPA, 20001).
The MCLG is then derived from the RfD as follows:
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Where:
bw = body weight (70 kg for adult \16\)
RSC = relative source contribution, the fraction of the RfD
allocated to drinking water
I = daily drinking water intake (2 liters for adults \16\)
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\16\ The MCLG for nitrite was based on a 4 kg body weight and a
0.64 liter drinking water intake for infants because they are the
group most sensitive to the critical effect.
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The relative source contribution (RSC) is one factor which will
determine how much a change in the RfD will lead to a change in the
MCLG. RSC refers to the method of accounting for human exposure from
multiple sources when setting health-based criteria. The purpose of
the RSC is to ensure that the level of a chemical allowed by a
criterion or multiple criteria, when combined with other identified
sources of exposure common to the population of concern, will not
result in exposures that exceed the RfD. The policy of considering
multiple sources of exposure when deriving health-based criteria has
become common in EPA's risk characterizations, as well as criteria
and standard-setting actions. The drinking water program has applied
a ceiling level of 80 percent of the RfD and a floor level of 20
percent of the RfD. That is, the MCLG cannot account for more than
80 percent of the RfD, nor less than 20 percent of the RfD. EPA
applies an RSC factor of 20 percent to the RfD when adequate
exposure data do not exist.
EPA has now revised its RSC method to improve consistency when
considering non-water sources of exposure (both ingestion exposures
(e.g., food) and exposures other than the oral route (e.g.,
inhalation). The approach is called the Exposure Decision Tree. RSC
estimates will be made by EPA using this approach, which allows for use
of either subtraction or percentage methods, depending on chemical-
specific circumstances, within the 20 to 80 percent range described in
the previous paragraph. For a detailed discussion on the revised
approach, refer to the ``Methodology for Deriving Ambient Water Quality
Criteria for the Protection of Human Health'' (USEPA, 2000f).
It has also been the Agency policy to apply an additional safety
factor to the RfD for chemicals with equivocal evidence of
carcinogenicity. This practice is another factor that must be evaluated
to determine the impact of a change in RfD on the MCLG.
For drinking water contaminants regulated prior to the 1996 SDWA,
EPA's Office of Water (OW) followed a three-category regulatory cancer
classification system (Categories I, II, or III). These categories
specify decisions as to degree of concern for an agent's carcinogenic
potential as a contaminant of drinking water, and define to some extent
the approach to risk management which is taken for establishing MCLGs.
Categories I, II, and III are designations not defined in guidelines
but which reflect OW policy.
EPA used the six alphanumeric categories (A, B1, B2, C, D, E) of
the 1986 cancer guidelines (51 FR 33992, September 24, 1986 (USEPA,
1986b)) in establishing the MCLG. The six-group classification system
is often equated to the three-category system in the National Primary
Drinking Water Regulation (NPDWR) Federal Register announcements. Table
A-1 describes the three categories and, with few exceptions (e.g.,
beryllium), their usual equivalent alphanumeric classification. If a
chemical is a known or probable human carcinogen (Category I, generally
Group A or B), the MCLG is generally set at zero because it is assumed,
in the absence of other data, that there is no known threshold for
carcinogenicity. If a chemical falls in Group C, an RfD approach along
with an additional safety (risk management) factor is used in deriving
the MCLG. The methodology used for establishing MCLGs for chemicals
with varying degrees of evidence of carcinogenicity is also briefly
described in Table A-1.
Recent Agency assessments also use the 1996 Proposed Guidelines for
Carcinogen Risk Assessment (61 FR 17960, April 23, 1996 (USEPA,1996))
or the draft revised Guidelines for Carcinogen Risk Assessment (USEPA,
1999b). The proposed guidelines use standard descriptors as part of the
hazard narrative to express the weight-of-evidence for carcinogenic
hazard potential. The 1996 descriptors are in three categories:
``Known/likely,'' ``cannot be determined,'' and ``not likely.''
Subdescriptors are provided under these categories to further
differentiate an agent's carcinogenic potential. The new descriptors
permit consideration of exposure route and mode of action when making
an assessment of carcinogenicity. The hazard descriptors of the 1996
proposed Guidelines are given in the text to this action whenever
appropriate. None of the chemicals discussed in this action have been
evaluated under the 1999 draft revised Guidelines for Carcinogen Risk
Assessment.
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[FR Doc. 02-9154 Filed 4-16-02; 8:45 am]
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